Resistors & Ohm's Law
Colour bands both ways, series and parallel networks, dividers, and nearest preferred values. Every resistance field reads 4k7 and 0R22 as happily as 4700 and 0.22.
Colour code
four, five or six bands
Resistance
—
Type a value to get its bands, or pick bands to get the value. Both directions stay in step.
Preferred values
for the coded resistance
E12 is ±10 % stock, E24 ±5 %, E96 ±1 %.
Series & parallel
Separated by commas, spaces or plus signs. A zero-ohm member is a link, and shorts the parallel combination.
- In series
- —
- In parallel
- —
- Nearest preferred, series
- —
- Nearest preferred, parallel
- —
Voltage divider
Vout is across R2
V
- Output
- —
- Current
- —
- Power in R1
- —
- Power in R2
- —
LED series resistor
V
V
About 2.0 V red, 3.2 V blue, green and white.
mA
- Exact value
- —
- Next preferred up
- —
- Current with it
- —
- Power in the resistor
- —
Notes
- Band colours are drawn and named. Colour is the whole content of a resistor code, so it is never the only channel here: every band appears as a swatch, a colour name and the number it stands for.
- The fourth band on a five-band code is the multiplier, not the tolerance — brown-black-black reads 10 Ω on four bands and 100 Ω on five.
- Round an LED ballast resistor up to the next preferred value. Rounding down raises the current above what you asked for.
- Nothing here accounts for a resistor's power rating. Compare the dissipated power against the part's rating with room to spare.