Resistor Symbol
Definition: The Resistor symbol represents a passive two-terminal component that opposes the flow of electric current, drawn as a zigzag line in ANSI Y32.2 / IEEE 315-1975 or as a plain rectangle in IEC 60617-04, with resistance measured in ohms (Ω); it is assigned the schematic designator R.
Also known as: resistance symbol, ohmic resistor symbol, fixed resistor symbol, zigzag resistor (ANSI informal), R symbol schematic.
What the Resistor symbol means
The resistor symbol denotes a component that converts electrical energy into heat by impeding current flow, with the degree of opposition quantified in ohms (Ω). In a circuit diagram, the resistor symbol tells the reader that current through that branch is limited or divided in proportion to Ohm's Law (V = IR).
Resistor symbols appear in virtually every circuit schematic because resistors perform foundational functions: setting bias points for transistors, forming voltage dividers, limiting current through LEDs, and providing pull-up or pull-down paths for logic signals. The resistor symbol's designator letter R is followed by a sequential number (R1, R2 …) and a value annotation such as 4.7 kΩ.
How to identify the Resistor symbol
In ANSI Y32.2 / IEEE 315-1975, the resistor symbol is drawn as a horizontal zigzag line — typically six equal peaks — spanning between two short lead lines that connect to the rest of the circuit. In IEC 60617-04, the same component is shown as a plain narrow rectangle (a box, approximately 3:1 width-to-height ratio) with lead lines extending from the two short ends. Both glyphs are horizontally oriented by convention, though they may be rotated 90° for vertical placement on a diagram. The ANSI zigzag and IEC rectangle are the two universally recognised forms; no other common electrical symbol uses a plain rectangle at this aspect ratio, making the IEC form unambiguous in context.
Function and usage boundary
A resistor opposes the flow of electric current through a circuit according to Ohm's Law: the voltage drop across the resistor equals the current through it multiplied by its resistance (V = I × R). This opposition converts electrical energy into thermal energy (heat). By selecting the appropriate resistance value, a circuit designer controls current magnitude, sets voltage levels through division, establishes time constants in RC networks, and provides impedance matching between circuit stages.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-04 (Binary Logic Elements, Passive Components) designates the resistor with a narrow filled rectangle and lead lines at each short end; the standard is maintained by the International Electrotechnical Commission and accessible via the IEC 60617 online database. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 (reaffirmed as IEEE 315-1975 and IEEE 315A-1986) designates the resistor with a six-peak zigzag line between two short lead lines; this form dominates schematics produced in the United States, Canada, and Japan (JIS C 0617 historically used the same zigzag before adopting the IEC rectangle in later editions). |
| Key difference | The ANSI / IEEE 315 resistor symbol is a zigzag line; the IEC 60617 resistor symbol is a plain rectangle. The two glyphs are functionally identical — both represent the same passive component — but are visually distinct, so mixed-standard diagrams must label which convention is in use. |
The displayed SVG is the live editor implementation, not a licensed reproduction or certification of an IEC or IEEE database glyph. Verify the exact official entry and project edition before issuing work.
Logical terminals
| Logical ID | Editor terminal name |
|---|---|
| a | A |
| b | B |
Where the Resistor symbol is used
- Current-limiting resistors in series with LEDs to prevent excess current (e.g. a 330 Ω resistor with a 3 V LED on a 5 V supply)
- Voltage dividers formed by two resistors in series to produce an intermediate reference voltage for ADC inputs
- Pull-up and pull-down resistors (typically 1 kΩ – 100 kΩ) on digital logic lines to define idle-state logic levels
- Biasing networks in transistor amplifier stages to set the quiescent operating point
- RC timing circuits combined with a capacitor to set oscillation frequency or time delays
- Sense resistors (shunt resistors, typically milliohm range) in current-measurement circuits
- Termination resistors (e.g. 50 Ω or 120 Ω) on transmission lines to prevent signal reflections
Key facts
- The resistor symbol is a zigzag line in ANSI Y32.2 / IEEE 315-1975 and a plain rectangle in IEC 60617-04; both represent the same passive component.
- The schematic designator for a resistor is R; individual resistors in a schematic are labelled R1, R2, R3 … in sequence.
- Resistance is measured in ohms (Ω), defined as the opposition to current flow that produces a 1 V drop when 1 A passes through (Ohm's Law: V = I × R).
- A resistor is a two-terminal, non-polar component; its two pins are labelled A and B (or simply the two lead ends) and it can be connected in either orientation without affecting function.
- Preferred resistance values follow the E-series (E12, E24, E48, E96, E192) defined in IEC 60063, covering tolerances from ±10 % down to ±0.5 %.
- Through-hole resistors use colour-band codes standardised in IEC 60062 to indicate value and tolerance; a 4-band resistor has three value bands and one tolerance band.
- Resistors dissipate energy as heat; power rating in watts (W) must exceed the product P = I² × R to prevent thermal failure.
- Variable resistors (rheostats, potentiometers) are shown with an arrow or slider modifier on the basic rectangle or zigzag symbol, per IEC 60617-04 and IEEE 315.
Diagrams that use this symbol
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Frequently asked questions
What does the resistor symbol look like?
The resistor symbol looks like a horizontal zigzag line (six peaks) in ANSI Y32.2 / IEEE 315-1975, used in the United States, Canada, and older JIS schematics. In IEC 60617-04, used throughout Europe and internationally, the resistor symbol is a plain narrow rectangle with lead lines on each short end. Both versions have the same meaning.
What does the resistor symbol mean in a circuit diagram?
The resistor symbol means that a component at that location imposes a specific opposition to current flow, quantified in ohms (Ω). The value printed beside the symbol (e.g. '4.7 kΩ') tells you the resistance. According to Ohm's Law (V = I × R), the symbol signals that current through that branch will equal the applied voltage divided by the stated resistance.
What is the difference between the IEC and ANSI resistor symbols?
The IEC 60617 resistor symbol is a plain rectangle; the ANSI Y32.2 / IEEE 315 resistor symbol is a zigzag line. The visual difference is significant — they are the two most commonly confused glyph differences between standards — but both symbols represent an identical component. European and international schematics use the rectangle; North American schematics use the zigzag.
What letter designates a resistor on a schematic?
The designator letter for a resistor is R, as defined in IEEE 315-1975 and IEC 60617-04. Resistors are numbered sequentially: R1, R2, R3. The designator appears adjacent to the symbol on the schematic and is also used in the bill of materials.
What unit is resistance measured in?
Resistance is measured in ohms, symbol Ω (Greek capital omega), as defined in the International System of Units (SI) and IEC 80000-6. Common multiples used in schematics are kilohms (kΩ, 10³ Ω) and megohms (MΩ, 10⁶ Ω). A component marked '10k' on a schematic has a resistance of 10,000 Ω.
Is the resistor symbol polarised — does it matter which way it is connected?
No, a standard fixed resistor is non-polar. The resistor symbol has two identical terminals (pins A and B) and the component can be connected in either direction without affecting its resistance or behaviour. Only special resistor variants such as varistors or thermistors with rectifying junctions have polarity.
What standard defines the resistor symbol?
The resistor symbol is defined in IEC 60617-04 (passive components, published by the International Electrotechnical Commission) for the rectangle form, and in ANSI Y32.2-1975 / IEEE 315-1975 (reaffirmed 1993) for the zigzag form. Both standards are the authoritative references cited in engineering drawings worldwide.
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Physical components that use this symbol
A schematic symbol defines electrical intent; the physical profile adds package or panel dimensions and mounting data.
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