Resistor color code calculator

How to read the colour code

Each colour stands for a number: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8 and white 9. On a 4-band resistor, the first two bands are digits, the third is the multiplier (the number of zeros) and the fourth is the tolerance. Yellow, violet, red, gold is 4, 7, then two zeros: 4,700 Ω, or 4.7 kΩ, with a tolerance of 5%.

A 5-band resistor has three digit bands, then the multiplier and tolerance, which gives more precise values. A 6-band resistor adds a final band for the temperature coefficient. Gold and silver as multipliers divide by 10 and 100, for values below 10 Ω.

To work out which end to start from, look for the tolerance band, usually gold, silver or brown, which is often slightly separated from the others. If you're still unsure, measure the resistor with a multimeter.

Standard values

Resistors are made in standard series so that each value is a fixed percentage above the last. The E12 series (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82) suits 10% tolerance, E24 adds values in between for 5%, and E96 has 96 values per decade for 1% resistors. When a calculation gives an exact value, pick the nearest standard value, or combine two resistors in series or parallel. The Ohm's law calculator works out combinations.

Writing values: 4k7 and R47

Circuit diagrams often use the letter as the decimal point, so a smudge can't turn 4.7 kΩ into 47 kΩ. 4k7 is 4.7 kΩ, 2M2 is 2.2 MΩ, and R47 is 0.47 Ω. You can type values that way above. SMD resistors use printed codes instead: three digits like 472 mean 47 followed by two zeros, 4.7 kΩ.

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