Resistor color code reader

Formula

How it works

The first two (or three, in 5-band) colored bands give the significant digits, the next band is a power-of-ten multiplier, and the last band gives the tolerance - reading the fixed IEC 60062 color-to-value table, never a formula to estimate.

Worked example

The same calculation with the default values:

• Number of bands 4-band
• First band (1st digit) Brown
• Second band (2nd digit) Black
• Third band (3rd digit, 5-band only) Black
• Multiplier band Red
• Tolerance band Gold

1. significant digits = 1×10 + 0 = 10
2. value = 10 × 10^2 = 1,000 Ω
3. tolerance = ± 5%

Result: Resistance: 1,000 Ω · Tolerance: 5% · Minimum value: 950 Ω

Common mistakes

• Reading the bands starting from the wrong end - start from the band closest to one edge, not from the one nearest the gap before the tolerance band.
• Confusing the multiplier band's gold/silver (×0.1/×0.01) with the tolerance band's gold/silver (±5%/±10%) - the same two colors mean different things on different bands.
• Misreading faded brown/red or green/blue bands under poor lighting.