A schematic is a drawing of a circuit that uses small standard pictures, called symbols, for the parts and plain lines for the wires that join them. This page is a reference you can keep open while reading one: it explains how a schematic is read, then shows the common symbols grouped by kind of part, each with its name and a one-line note on what it stands for. Where a part has its own Learn article, the first symbol of that kind links to it.
How to use this page. Skim sections 1 and 2 once. After that, jump to the category you need from the list below. Each symbol is drawn the way it most often appears in hobby and US schematics; where the international (IEC) drawing differs, the note says so, and the most common variants have their own drawings.
A schematic shows how parts are connected and what each part does, using graphic symbols. It does not show how big the parts are, what they look like or where they sit on a circuit board. The U.S. Navy's training course puts it this way: the schematic is used to trace a circuit and its functions "without regard to the actual physical size, shape, or location" of the parts, and it is the most useful drawing for learning how a system works.[1] A drawing that shows where real wires and terminals go is a different thing, called a wiring diagram.
Because a symbol stands for a kind of part, the same zigzag means "resistor" whether the real part is a tiny surface-mount chip or a resistor as long as your finger. The text written beside the symbol (its name and value) says which exact part is meant.
Two families of symbols
Symbols are set by standards, which are agreed rulebooks published by engineering bodies. Two families matter for hobby work:
US (ANSI/IEEE) symbols. IEEE Std 315 (also published as ANSI Y32.2) lists graphic symbols and the letters used to name parts on electrical and electronics diagrams. Its symbols are drawn so their connection points fall on a grid, and it was written to be compatible with the international rules where possible.[2] It was reaffirmed in 1993 and is now listed by IEEE as inactive, but its drawings remain the basis of most US schematics.
International (IEC) symbols. IEC 60617, "Graphical symbols for diagrams," is kept by the International Electrotechnical Commission as an online database of more than 1,500 symbols, from conductors and passive parts to semiconductors, switchgear, measuring instruments and logic elements.[3] European and many Asian schematics use these.
Most symbols are the same in both families. The best-known difference is the resistor: a zigzag in US drawings and a plain rectangle in IEC drawings.[4] Fuses, relay coils and logic gates also differ, as the cards below show. Many schematics mix the two, so it pays to recognize both.
2. How to read a schematic
Figure 1 is a small circuit you could build: a battery, a switch, a resistor and a light-emitting diode (LED). It carries all the basic marks you will meet on any schematic. The DC Circuits article walks through reading a schematic like this one step by step.
Figure 1. A small schematic with its basic marks labeled. The battery BT1 drives current through switch S1, resistor R1 and LED D1, and back along the bottom wire; the dot after S1 is where the R1 and D1 branch leaves the top wire, which carries on to a net label named 9V.
Wires, nets and nodes
Each straight line is a wire: a perfect conductor joining the parts at its ends. The lines do not show real wire lengths or routes. Every point joined by wires, with no part in between, is at the same voltage, and that whole connected group is called a net (or a node).[4] In Figure 1, the top of R1, the switch output and the net label are all one net.
Junctions and crossings
Where a wire splits into two or more, it forms a junction, and a filled dot is drawn at that point. The dot is what says "these wires are connected." When two wires cross with no dot, they simply pass each other and are not connected.[4] Some older drawings show an unconnected crossing as a small hump, where one wire hops over the other. Because a dot can be lost when a drawing is copied or shrunk, careful designers avoid four wires meeting at one dot and use two T junctions a little apart instead (Figure 2).[4]
Figure 2. Junctions and crossings. A dot means connected; no dot means the wires just cross. Two offset T junctions are the clearest way to join four wires.
Labels, power symbols and ground
To keep a busy drawing readable, a wire can end in a net label: a name tag such as SDA or 9V. Every wire that carries the same name is connected, even with no line drawn between them.[4] Power and ground symbols are special labels of this kind. A short line topped by a bar or an arrow and labeled +5V or VCC joins that point to the positive supply, and a ground symbol joins it to the common return wire, so you rarely see the full supply wiring drawn out.[4] Section 6 shows these symbols.
Drawing habits worth knowing
Signal flow usually runs left to right: inputs on the left, outputs on the right.
Higher voltage at the top, ground at the bottom, so current tends to "fall" down the page.
Pin numbers on a chip symbol are the real pin numbers of the package, written next to each lead, often along with the pin's name.[4]
Polarity marks (a plus sign, a curved plate, the bar on a diode) show which way round a part must go.
3. Reference designators and values
Every symbol carries two pieces of text. The reference designator is a short unique name made of a letter code and a number, such as R1, R2 or C7, so that a parts list or a person can point at one exact part. The value says which part it is: ohms for a resistor, farads for a capacitor, a frequency for a crystal or a part number for a chip.[4] IEEE 315 includes the standard list of these letter codes.[2] The common ones are below; drawings do not always follow them, so you may see IC instead of U or XTAL instead of Y.[4]
Common reference-designator letters
Letters
Part
Letters
Part
R
Resistor
K
Relay
C
Capacitor
F
Fuse
L
Inductor (coil)
BT
Battery or cell
T
Transformer
J, P
Connector (J is usually the fixed jack, P the plug)
D
Diode or LED
LS
Loudspeaker
Q
Transistor
M
Motor
U
Integrated circuit
MK
Microphone
Y
Crystal or oscillator
TP
Test point
S or SW
Switch
CB
Circuit breaker
R, C, L, D, Q, U, Y and S are from SparkFun's list;[4] the others follow the IEEE 315 class letters and are the ones most often seen in practice.
4. Passive components
A passive component can store, resist or pass on energy but cannot add energy or amplify a signal. Resistors, capacitors, inductors and transformers are the main ones. Each has two or more leads (connection wires), drawn as the short straight lines at the ends of the symbol.
Resistor (US)A part that limits current, turning the extra energy into heat. The zigzag is the US form.[4]ResistorsResistor (IEC)The same part in international drawings: a plain rectangle. IEC-style values often put the multiplier letter where the decimal point goes, so 4k7 means 4.7 kΩ.[5]Variable resistor (rheostat)A two-lead resistor whose value can be changed; the diagonal arrow means "adjustable."[4][1]PotentiometerA resistor with a third lead, the wiper, that slides along it; the arrow is the wiper.[4]Variable resistorsCapacitorTwo plates separated by an insulator; it stores charge. Two straight plates mean it can go in either way round.[4]CapacitorsPolarized capacitorAn electrolytic or tantalum capacitor that must go in one way round. The curved plate is the negative side and a plus marks the positive.[4] Some drawings use a hollow box for the positive plate instead.Variable capacitorA capacitor whose value can be adjusted, as in an old radio tuning knob; the arrow again means "adjustable."Inductor (coil)A coil of wire that stores energy in a magnetic field. Drawn as loops or bumps; some older IEC drawings use a filled rectangle.[4]CoilsIron-core inductorSolid lines beside the coil show a core of iron or steel laminations, which raises the inductance; the transformer symbol uses the same lines.[1]Ferrite-core inductorDashed lines usually mean a ferrite (ceramic magnetic) core, common in high-frequency coils and chokes.TransformerTwo coils sharing a magnetic core: the primary takes power in and the secondary delivers it. The dots mark winding ends that have the same polarity at the same instant.[4][6]TransformersAntennaA conductor that sends or receives radio waves. This branched "Y" is the general form; antennas were one of the main areas expanded in IEEE 315-1975.[2]
5. Semiconductors
A semiconductor device is made from a material such as silicon whose ability to conduct can be controlled, which lets it steer current one way (a diode) or switch and amplify (a transistor). Its symbol always shows direction. In diode symbols the triangle points the way conventional current flows (from plus to minus), from the anode (A) to the cathode (K, from the German spelling Kathode); the bar is the cathode.[4][7]
DiodeLets current flow from anode to cathode and blocks it the other way. The bar matches the band printed on the real part.[4]DiodesSchottky diodeA fast diode with a low forward voltage, used in power supplies; the bar has small hooks like an S.[4]Kinds of diodeZener diodeBuilt to conduct backward at a set voltage, so it can hold a voltage steady; the bar's bent ends suggest a Z.[7][8]Zener regulatorLight-emitting diode (LED)A diode that gives off light when current flows forward; the two arrows point away, light leaving.[7]LEDsPhotodiodeA diode that passes a current in proportion to the light falling on it; the arrows point in, light arriving.[7][4]PhotodiodesNPN transistorA bipolar transistor: a small base (B) current controls a larger collector (C) to emitter (E) current. The emitter arrow points out ("Not Pointing iN").[4]Transistor symbolsPNP transistorThe mirror image of the NPN, working with the opposite polarity; its emitter arrow points in, and the emitter is usually drawn at the top, toward the positive supply.[4][7]N-channel MOSFETA voltage on the gate (G) switches current between drain (D) and source (S). The broken line is an enhancement-mode channel; the arrow points in for N-channel.[4][7] Power MOSFET symbols often add a built-in body diode.[9]MOSFETsP-channel MOSFETThe opposite polarity: the arrow points out, and the source usually sits at the top, toward the positive supply.[4] Many drawings simplify both MOSFETs to three leads with an arrow on the source.N-channel JFETA junction field-effect transistor: a solid channel bar with the gate arrow pointing in. In JFET symbols the arrow always points toward the N-type material.[7]JFETsP-channel JFETThe same outline with the gate arrow pointing away from the channel.[7]Thyristor (SCR)A silicon-controlled rectifier: a diode that stays off until a pulse on its gate (G) turns it on, then stays on until the current stops.[7]TriacWorks like two SCRs back to back, so it can switch AC in both directions. The leads are main terminals MT1 and MT2 and the gate; MT1 is on the gate side.[7]Optocoupler (optoisolator)An LED and a light sensor (here a phototransistor) sealed in one package, so a signal can cross by light with no electrical connection. The dashed box shows the package; pin numbers follow the 4N35.[10][7]Optocouplers
6. Sources, power and ground
A source supplies energy to the circuit. A DC (direct current) source keeps a steady polarity, like a battery; an AC (alternating current) source reverses polarity many times a second, like a wall outlet. The ground symbols mark the common reference point that voltages are measured from, and they come in several kinds that do not all mean the same thing.
CellOne electrochemical cell. The long thin plate is positive and the short thick plate is negative.[4]Cell or battery?BatterySeveral cells in series. More plate pairs usually means more cells, though drawings often show two pairs for any battery.[4][1]DC voltage sourceA supply that holds a steady voltage, such as a bench power supply; the signs show its polarity.[4]AC voltage sourceA supply whose voltage swings up and down, such as mains power or a signal generator; the sine wave shows the shape.[4]The sine waveCurrent sourceAn ideal supply that pushes a set current, whatever voltage that takes; mostly seen in textbook and simulation drawings.Power rail (supply label)A one-lead symbol that joins a point to the named supply, such as +5 V or VCC; positive rails usually point up.[4]Ground (earth)The general ground symbol. In IEC 60417 (symbol 5017) it marks an earth connection; on most electronics schematics it simply means the circuit's 0 V return.[11][4]GroundChassis (frame) groundA connection to the metal frame or case (IEC 60417 symbol 5020).[11] The frame is at earth potential only if it is wired (bonded) to earth.Signal (common) groundA triangle (or downward arrow) used by some drawings for the circuit's common return.[4]Protective earthThe terminal for the safety earth wire that guards against shock if a fault occurs (IEC 60417 symbol 5019).[11] Seen on mains equipment, not low-voltage boards.
7. Switches, relays and protection
A switch opens or closes a path for current. Its type is described by poles (how many separate circuits it controls) and throws (how many positions each pole can connect to): SPST means single-pole, single-throw.[4] Symbols show the normal state: the way the switch sits on the shelf, unpressed and unpowered.[12] Protection parts open the circuit or absorb a surge when something goes wrong.
SPST switchAn on/off switch: one blade, one contact. Open as drawn.[4]Poles and throwsSPDT switchOne common (COM) terminal connects to either of two others, A or B, like a two-way light switch. Ganged poles of one switch are joined by a dashed line.[4]Pushbutton, normally openConnects only while pressed, like a doorbell button; a spring returns it.[13][12]Normally open or closedPushbutton, normally closedConnected at rest, and breaks the circuit while pressed, as in a stop button.[13][12]RelayAn electrically operated switch: current in the coil moves the contacts. The rectangle is the coil (US drawings may show a circle or a coil instead); the dashed line links it to the contacts it moves.[4][13][14]RelaysFuse (US)A thin link that melts and opens the circuit when the current is too high. The S-curve is the older US form.[15][1]FusesFuse (IEC)A rectangle with the wire running through it; now common in US schematics too.[13][15] A plain rectangle without the line would be an IEC resistor.Circuit breakerA switch that trips open on overcurrent and can be reset by hand. IEC drawings show a switch with a small × on its contact.[15][13]BreakersResettable fuse (PTC, polyfuse)Drawn as a thermistor: its resistance jumps when it heats up, limiting the current until it cools.[4]PolyfusesTVS diodeA transient-voltage suppressor clamps short voltage spikes. Unidirectional parts (top) look like a Zener; bidirectional parts (bottom) clamp both ways and have no cathode band.[16]TVS diodes
8. Analog parts and integrated circuits
An integrated circuit (IC, or chip) holds many transistors and other parts on one piece of silicon. Most ICs have no special symbol: they are drawn as a rectangle with each pin labeled by number and name.[4] A few very common ones have their own shapes or a standard layout.
Operational amplifier (op-amp)Amplifies the difference between its inverting (−) and non-inverting (+) inputs. Supply pins are often left off and drawn once elsewhere.[4][17]Op-amps555 timerDrawn as a box. The pin names are TRIG (trigger), THR (threshold), DIS (discharge), OUT, RST (reset), CV (control voltage), plus VCC and GND; the numbers are the 8-pin package pins.[18]The 555Voltage regulatorA three-pin box: input on the left, output on the right, ground (or adjust) at the bottom.[4] Numbers are the TO-220 pins of a 7805.[19]Fixed regulatorsCrystalA quartz crystal that sets a steady clock frequency; the rectangle between plates is the quartz.[4]CrystalsCeramic resonatorA cheaper, less exact clock part. The three-pin type has the two load capacitors built in, with the middle pin going to ground.[4]ResonatorsGeneric ICAny chip without its own symbol: a rectangle, a designator such as U3 and a part number, with every pin numbered and usually named.[4]Pin numbering
9. Digital logic
Digital circuits work with just two levels: high (logic 1) and low (logic 0). A logic gate takes one or more inputs and sets its output by a fixed rule. US schematics use distinctive shapes, one outline per rule.[20] A small circle, called a bubble, on an output or input means "inverted": it turns AND into NAND and OR into NOR.[4]Logic from transistors shows how gates are built.
BufferOutput equals input, but with more drive strength. The triangle is the amplifier shape.[20][21]NOT gate (inverter)Output is the opposite of the input: 1 becomes 0. The bubble does the inverting.[20]AND gateOutput is 1 only when all inputs are 1.[20]NAND gateNOT-AND: output is 0 only when all inputs are 1.[20]OR gateOutput is 1 when at least one input is 1.[20]NOR gateNOT-OR: output is 1 only when every input is 0.[20]XOR gateExclusive OR: output is 1 when the inputs differ (for two inputs, exactly one is 1).[20]XNOR gateThe inverse of XOR: output is 1 when the inputs are the same.[20]IEC rectangular gatesIEEE Std 91 and IEC drawings use one rectangle for every gate and write the rule inside: & for AND, ≥1 for OR (at least one input), =1 for XOR (exactly one) and 1 with a bubble for NOT.[21]D flip-flopA one-bit memory: on each rising clock edge, Q copies D. The small triangle marks an edge-triggered clock input; Q-bar (Q with a line over it) is the opposite of Q. PRE and CLR force Q to 1 or 0; on the 74HC74 they are active-low, which some drawings show with bubbles.[22][20][21]MicrocontrollerA small computer on a chip. Like any IC it is a labeled box, often with pins grouped by job rather than in package order. Pin numbers here are the ATmega328P (Arduino Uno chip) in its 28-pin DIP.[23][4]Feeding a microcontroller
10. Meters, transducers and sensors
A meter measures a quantity in the circuit. A transducer turns one form of energy into another: a speaker turns electrical signals into sound, a microphone turns sound into signals, and a motor turns current into motion. A sensor is a transducer used to measure something, such as temperature or light. Meter symbols are a circle with letters inside naming what is measured.[15]
AmmeterMeasures current. It is placed in series, so the current flows through it.[15][24]VoltmeterMeasures voltage. It is connected in parallel, across the part being measured.[15][24]MeasuringOhmmeterMeasures resistance. The US standard writes OHM inside the circle; most drawings use the Ω sign instead.[15]LampA filament or indicator lamp. The circle with an X is the international form; older US drawings show a circle with short rays around it.[13]LoudspeakerTurns an electrical signal into sound. The symbol looks like the real part: a magnet and a cone.[4]SpeakersBuzzerMakes a tone. Buzzers have no single standard shape, and the bell-like dome is a common one; many have a polarity marked plus.[4]BuzzersPiezo elementA piezoelectric disc used as a buzzer or sensor, often drawn like a crystal because it works by the same piezoelectric effect. PiezoMicrophoneTurns sound into an electrical signal; usually drawn as a circle with a bar along one side, the bar standing for the diaphragm. MicrophonesMotorA circle with M (older US drawings write MOT).[4][1] IEC drawings add the number of phases, as in M 1~.[13]DC motorsThermistorA resistor that changes with temperature: the slanted line means "changes by itself," t° means temperature. −t° marks an NTC (resistance falls as it warms).[1][4]ThermistorsPhotoresistor (LDR)A light-dependent resistor (the Navy course calls it a photocell): a resistor with light arrows pointing in.[7]PhotoresistorsSensor module (generic)There is no single "sensor" symbol. ICs such as Hall-effect sensors are drawn as a labeled box with power, ground and output pins.[4]Hall sensors
11. Connectors and miscellaneous
These marks describe connections rather than parts: how wires join, cross and leave the board, and where you can probe it.
Wire (conductor)A perfect connection between its ends; length and route mean nothing.[4]Junction (node dot)A dot where wires meet means they are connected.[4]Crossing, not connectedWires that cross with no dot (left) do not connect. The hop (right) is an older way to show the same thing.[4]Net labelWires carrying the same name are connected, even far apart or on another sheet.[4]Test pointA pad or pin left for probing with a meter or oscilloscope, named TP1, TP2 and so on; the Raspberry Pi Pico has six.[25]Header or connectorA rectangle with numbered pins, named J1, P1 and so on; the drawing varies with the connector style.[4]No-connect markAn X on a pin says it is deliberately left unconnected, not forgotten. Datasheets label such pins NC; pin 3 of the 4N35 is one.[10]
12. Reading an unfamiliar symbol
No reference lists every symbol; IEC 60617 alone has more than 1,500.[3] When you meet one you do not know, these steps usually work:
Read the designator. The letter (R, C, Q, U, K…) tells you the family even when the drawing is odd.[4]
Read the value or part number and look up that part's datasheet; datasheets usually show the symbol and every pin.
Look for modifiers on a familiar shape. An arrow across means adjustable, arrows in mean light-sensitive, arrows out mean light-emitting, a slanted line with t° means temperature-dependent, and a bubble means inverted.[4][7][20]
Check which family the drawing uses. A rectangle might be an IEC resistor, an IEC fuse (line through it), an IEC relay coil or a logic gate (symbol inside). The surrounding symbols usually show which.[13][21]
Check the drawing's own key. Large schematics often include a legend of the symbols they use.
All links were checked in October 2026. External links open in a new tab.
U.S. Navy, NEETS Module 4: Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading, chapter 3, "Schematic diagram", and Appendix II, "Electrical and Electronic Symbols" (PDF): https://legacy.maritime.org/doc/neets/mod04.pdf
IEEE Standards Association, "IEEE/ANSI 315-1975: IEEE Standard for Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters)" (standard summary page; the standard itself is sold by IEEE): https://standards.ieee.org/ieee/315/515/
International Electrotechnical Commission, "IEC 60617 DB: Graphical symbols for diagrams" (database summary page; access is by subscription): https://webstore.iec.ch/en/publication/2723
U.S. Navy, NEETS Module 2: Introduction to Alternating Current and Transformers, chapter 5, "Producing a Counter EMF" and phase-indicating dots (Integrated Publishing reprint): https://tpub.com/neets/book2/5e.htm
U.S. Navy, NEETS Module 7: Introduction to Solid-State Devices and Power Supplies, chapters 1 to 3 (diode, transistor, Zener, optoelectronic, SCR, TRIAC, JFET and MOSFET symbols; PDF): https://legacy.maritime.org/doc/neets/mod07.pdf
U.S. Navy, NEETS Module 3: Introduction to Circuit Protection, Control, and Measurement, chapter 2 (fuse and circuit-breaker symbols) and Appendix III, "Schematic Symbols" (PDF): https://legacy.maritime.org/doc/neets/mod03.pdf
U.S. Navy, NEETS Module 13: Introduction to Number Systems and Logic Circuits, chapters 2 and 3 (logic gates, inverters and flip-flops; PDF): https://legacy.maritime.org/doc/neets/mod13.pdf