What this calculator does
A resistor colour code is how a resistor prints its value on its own body, since it is usually too small to fit readable text. This resistor calculator reads the bands the way you would with a chart in hand: pick the colour of each band, and it works out the resistance and the tolerance that go with them.
Most resistors carry four bands: two digits, a multiplier, and a tolerance. Precision resistors often carry five, with three significant digits instead of two, which lets them state a more exact value before the multiplier is applied. Both layouts follow the same fixed, industry-standard colour code, so a given set of bands always means the same number.
The formula
Each colour stands for a digit from 0 to 9 (black through white). On a 4-band resistor, the first two bands give the two significant digits, the third band is the multiplier, and the fourth is the tolerance. On a 5-band resistor, the first three bands give three significant digits before the multiplier and tolerance bands. Multiply the digits by the multiplier to get the resistance in ohms, then apply the tolerance either side of that value.
| Term | Meaning |
|---|---|
| Digit bands | The first two (4-band) or three (5-band) bands, each standing for one digit of the value. |
| Multiplier band | The power of ten the digits are multiplied by, including gold (×0.1) and silver (×0.01) for resistors under 10 ohms. |
| Tolerance band | How far the actual resistance may vary from the printed value, commonly gold (±5%) or brown (±1%). |
The inputs explained
| Field | What to enter |
|---|---|
| Number of bands | Whether the resistor has 4 or 5 colour bands. |
| Band 1 (1st digit) | The first band, read from the end furthest from the tolerance band. |
| Band 2 (2nd digit) | The second band. |
| Band 3 (3rd digit, 5-band only) | The third band, only used for a 5-band resistor. |
| Multiplier band | The multiplier band, usually the second-to-last band. |
| Tolerance band | The tolerance band, usually set apart slightly from the others. |
When to use it
Identifying a resistor pulled from a drawer
A loose resistor with no packaging gives up its value only through its bands. Matching the colours in order, left to right, and reading them off here is faster than hunting for a multimeter.
Checking a resistor before fitting it
Reading the bands and confirming the resistance and tolerance match the circuit design catches a wrongly picked component before it is soldered in.
Learning the colour code itself
Working through a few known resistors and comparing the decoded value against the value printed on a multimeter reading is the fastest way to commit the sequence, black through white, to memory.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Common 4-band resistor values
A fixed first two digits (brown, black = 1, 0), across a range of multiplier bands, all with a gold tolerance band.
| Multiplier band | Resistance | Acceptable range |
|---|---|---|
| Black | 10.00 Ω | 9.50 Ω to 10.50 Ω |
| Red | 1.000 kΩ | 950.00 Ω to 1.050 kΩ |
| Orange | 10.000 kΩ | 9.500 kΩ to 10.500 kΩ |
| Yellow | 100.000 kΩ | 95.000 kΩ to 105.000 kΩ |
How the tolerance band changes the acceptable range
A fixed 1 kΩ value, across the range of standard tolerance bands.
| Tolerance band | Tolerance | Acceptable range |
|---|---|---|
| Silver | ±10.00% | 900.00 Ω to 1.100 kΩ |
| Gold | ±5.00% | 950.00 Ω to 1.050 kΩ |
| Red | ±2.00% | 980.00 Ω to 1.020 kΩ |
| Brown | ±1.00% | 990.00 Ω to 1.010 kΩ |
Questions
Which end do I start reading from?
Start from the band closest to one end, furthest from the tolerance band. The tolerance band (commonly gold or silver) is usually spaced slightly further from the rest, which marks it as the last band rather than the first.
What is the difference between a 4-band and 5-band resistor?
A 4-band resistor encodes two significant digits before the multiplier; a 5-band resistor encodes three, giving a more precise nominal value. Precision resistors, with tighter tolerances such as ±1%, are usually 5-band.
What does a missing tolerance band mean?
No fourth band at all (an older convention, now uncommon) traditionally meant a ±20% tolerance. Modern resistors almost always carry an explicit tolerance band.
Why do gold and silver appear as both multiplier and tolerance colours?
The colour code reuses gold and silver for two different jobs. As a multiplier they mean ×0.1 and ×0.01, for resistors under 10 ohms. As a tolerance band, further along, they mean ±5% and ±10%. Position on the resistor, not colour alone, tells you which job a given gold or silver band is doing.
For working out voltage, current or power once you know the resistance, see the Ohm’s law calculator. To combine several resistors in series or parallel, use the resistors in series and parallel calculator.