Resistor Colour Code Calculator

Resistors use a standard colour-band system to mark their resistance value because the tiny components are too small to print numbers on reliably. The Electronic Industries Alliance (EIA) colour code maps ten colours to the digits 0 through 9, a set of multipliers, and tolerance values. On a 4-band resistor, the first two bands each represent a digit, the third band is a multiplier (how many zeros to add), and the fourth band shows the tolerance, which is how accurate the actual value is compared to the marked value. Reading from left to right, you form a two-digit number from the first two bands, multiply by the third band's multiplier, and then note the tolerance percentage from the fourth band. This calculator does the lookup for you. Select the colour of each band from the four dropdown menus and the result updates instantly. You get the nominal resistance in ohms (or kilohms or megaohms for large values), the tolerance percentage, and the actual resistance range the component will fall within. For example, Red Red Brown Gold gives 2, 2, multiplier 10, tolerance 5%, meaning 220 ohms plus or minus 5%, with a range of 209 ohms to 231 ohms. The tool covers the standard EIA 4-band code used on most carbon-film and metal-film resistors. Five-band and six-band resistors used in precision applications have a slightly different scheme.

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Band 1 (first digit)

Band 2 (second digit)

Band 3 (multiplier)

Band 4 (tolerance)

220 Ω

nominal resistance

Tolerance±5%

Minimum209 Ω

Maximum231 Ω

How it works

The first digit band and second digit band form a two-digit number (10 times band1 plus band2). That number is multiplied by the band3 multiplier to give the nominal resistance in ohms. The tolerance band gives the percentage plus or minus. Minimum resistance is the nominal value times (1 minus tolerance/100) and maximum is the nominal value times (1 plus tolerance/100). Values of 1,000 ohms or more are displayed in kilohms; values of 1,000,000 ohms or more in megaohms.

Worked example

Select Red, Red, Brown, Gold. Band 1 is Red = 2, Band 2 is Red = 2, so the two-digit number is 22. Band 3 is Brown = x10. Nominal value = 22 times 10 = 220 ohms. Band 4 is Gold = plus or minus 5%. Range: 220 times 0.95 = 209 ohms minimum, 220 times 1.05 = 231 ohms maximum. These match the default selections above.

Related calculators

Series and Parallel Resistance Calculator: combine multiple decoded resistor values in a circuit.
Ohm's Law Calculator: apply the decoded resistance value to solve V=IR.
Percent Error Calculator: compare a measured resistance against the nominal colour-code value.

Frequently asked questions

How do I read a 4-band resistor colour code?

On a 4-band resistor, the first two bands are digits (0 through 9), the third band is a multiplier (a power of 10), and the fourth band is the tolerance. Read the digit bands left to right, form a two-digit number, multiply by the multiplier, then note the tolerance. For example, Red Red Brown Gold means 2, 2, times 10, plus or minus 5 percent, giving 220 ohms.

What do the resistor colour code colours mean?

Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9 for digit bands. Multipliers use the same colours but as powers of ten (Black=1, Brown=10, Red=100, etc.). Gold and Silver also serve as multiplier bands (Gold = x0.1, Silver = x0.01). As tolerance bands, Gold is plus or minus 5 percent and Silver is plus or minus 10 percent; no fourth band means plus or minus 20 percent.

What is the resistance range for a 220-ohm 5% resistor?

A 220-ohm resistor with 5% tolerance can have an actual resistance anywhere from 220 minus 5 percent (209 ohms) to 220 plus 5 percent (231 ohms). This range matters when designing precision circuits where exact values are important.