Resistor Calculators
Resistor Color Code Calculator
Choose the band colours and read the resistance, tolerance range and temperature coefficient, with the resistor drawn as you go.
Resistor Colour Code
Pick each band colour. The value updates as you choose.
How the Colour Code Works
The IEC colour code encodes a resistor's value in printed bands. Each colour maps to a digit, a multiplier, a tolerance or a temperature coefficient, depending on the position of the band.
In a 4-band resistor the first two bands are significant digits, the third is the power-of-ten multiplier and the fourth is the tolerance. A 5-band resistor adds a third significant digit, giving finer resolution for precision parts. A 6-band resistor adds a final band for the temperature coefficient in parts per million per kelvin.
| Colour | Digit | Multiplier | Tolerance | Temp. coefficient |
|---|---|---|---|---|
| Black | 0 | ×1 | — | — |
| Brown | 1 | ×10 | ±1% | 100 ppm/K |
| Red | 2 | ×100 | ±2% | 50 ppm/K |
| Orange | 3 | ×1 k | — | 15 ppm/K |
| Yellow | 4 | ×10 k | — | 25 ppm/K |
| Green | 5 | ×100 k | ±0.5% | — |
| Blue | 6 | ×1 M | ±0.25% | 10 ppm/K |
| Violet | 7 | ×10 M | ±0.1% | 5 ppm/K |
| Grey | 8 | ×100 M | ±0.05% | — |
| White | 9 | ×1 G | — | — |
| Gold | — | ×0.1 | ±5% | — |
| Silver | — | ×0.01 | ±10% | — |
How to Use the Resistor Color Code Calculator
Pick the number of bands first. The band selectors change to match: four bands show two digits, a multiplier and a tolerance; five bands add a third digit; six bands add a temperature coefficient.
Set each dropdown to the colour you see on the component. A colour swatch beside every selector confirms your choice, and the drawn resistor above updates immediately, so you can compare it against the part in your hand. The value recalculates on every change; there is no separate calculate step.
Reading direction matters. Hold the resistor so the tolerance band, which is usually gold or silver and often separated by a wider gap, is on the right. Read from left to right from there. If both ends look similar, the band closest to a lead is normally the first digit.
Worked Example: Decoding a Four-Band Resistor
Take a 4-band resistor marked brown, black, red, gold.
Brown is 1 and black is 0, giving the significant digits 10. Red as a multiplier is ×100, so the value is 1 kΩ. Gold gives a tolerance of ±5%, meaning the actual part lies somewhere between 950 Ω and 1050 Ω.
A 5-band example: brown, black, black, brown, brown. The digits are 1, 0 and 0, giving 100; the brown multiplier is ×10, so the value is again 1 kΩ, but the brown tolerance band narrows the range to ±1%, or 990 Ω to 1010 Ω. Precision parts are marked this way because a fourth colour is needed to express the tighter tolerance.
Reading Your Color Code Results
The resistance figure is the nominal value the manufacturer aimed for. The tolerance tells you how far from that figure the real part is permitted to be, and the minimum and maximum tiles show that range as actual resistances rather than a percentage.
That range is often more important than the nominal value. In a voltage divider, two 5% resistors can combine to shift the output by several per cent, which is why 1% parts are specified where the ratio matters. In a current-limiting application, the tolerance simply shifts the current slightly and rarely causes a problem.
For 6-band resistors, the temperature coefficient in parts per million per kelvin describes how much the value moves as the part heats up. A 100 ppm/K resistor of 10 kΩ changes by 1 Ω per degree, which is negligible in most circuits and significant in precision measurement.
Where the Resistor Color Code Is Used
The immediate use is sorting an unlabelled parts drawer. Reading bands is faster than metering every component, and the drawn resistor makes it easy to confirm you have interpreted the order correctly before committing a part to a board.
The tolerance information guides substitution. If a design calls for 4.7 kΩ and you have a 4.7 kΩ part with a silver band, you are working with ±10%, and in a timing circuit that error carries straight through to the frequency. Knowing that in advance is the difference between a circuit that works and one that needs trimming.
Finally, the code helps when reverse-engineering an existing board, where reading the bands is often quicker than desoldering a part to measure it in isolation.
Limits of Color Code Decoding
- Colour perception is unreliable on small or aged components. Brown and red, and orange and red, are commonly confused under warm lighting. Confirm anything critical with a meter.
- Resistors soldered into a circuit cannot be measured accurately in place, because parallel paths on the board alter the reading. Lift one lead first.
- Some parts, particularly surface-mount and high-precision types, use printed numeric codes rather than bands and are not covered here.
- The bands describe resistance only. Power rating, voltage rating and construction type come from the physical size and the datasheet, not from the colours.
Questions
Resistor Color Code FAQs
Which end of the resistor do I read first?
Read from the end where the bands are grouped closest together, with the tolerance band, usually gold or silver and often set slightly apart, on the right.
What is the difference between a 4-band and a 5-band resistor?
A 5-band part carries a third significant digit, which allows finer values and usually indicates a tighter tolerance. The multiplier and tolerance bands follow the digits in both cases.
What does the sixth band mean?
It gives the temperature coefficient in parts per million per kelvin, describing how far the resistance drifts as the component warms up. It only appears on precision parts.
Why does my meter read slightly differently from the calculated value?
Tolerance accounts for most of it, and meter accuracy and lead resistance for the rest. As long as the reading falls between the minimum and maximum shown, the part is within specification.
Put the Decoded Value Into the Ohms Law Wheel
Open the full Ohms Law Wheel calculator to solve voltage, current, resistance and power from any two known values.