This resistor color code calculator decodes the colored bands on a resistor into its resistance value and tolerance — pick the colors, get the ohms, no memorized mnemonics required.
How to Read Resistor Bands
Resistors are too small for printed numbers, so the industry paints the value on: colored stripes read from the end opposite the tolerance band (usually gold or silver, and set slightly apart). On a 4-band resistor: digit, digit, multiplier, tolerance. On a 5-band (precision) resistor: three digits, then multiplier, then tolerance. The digits follow the rainbow’s dark end: Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Grey 8, White 9 — generations of technicians learned it via mnemonics of varying politeness. Pair the decoded value with our Ohms Law Calculator to put it to work. Part of our Physics Calculators collection.
Worked Example (Verified)
Yellow – Violet – Brown – Gold (the defaults above):
- Digits: 4, 7 → “47”; multiplier Brown = ×10
- Value: 47 × 10 = 470 Ω
- Gold tolerance ±5% → the actual resistor measures anywhere in 446.5–493.5 Ω and is in spec — tolerance is a promise about a range, not an admission of sloppiness
- The classic companion: Red–Red–Brown–Gold = 22 × 10 = 220 Ω, the current-limiting workhorse of a thousand LED circuits
Practical Reading Tips
- Direction matters: reading backwards turns 470 Ω into a nonsense (or worse, plausible wrong) value. Find the tolerance band first — it is usually metallic and offset — and read away from it.
- Heat discolors: a cooked resistor’s red can masquerade as brown or orange. When a circuit has failed hot, measure with a multimeter instead of trusting your eyes.
- Gold and silver only appear as multipliers (×0.1, ×0.01) or tolerance bands, never as leading digits — a built-in error check.
- Surface-mount resistors use printed codes instead (e.g. “472” = 47 × 10² = 4.7 kΩ — same digit–digit–multiplier logic in disguise).
Related Tools
- Ohms Law Calculator — voltage, current, resistance, power
- Physics Calculators — the full collection
Frequently Asked Questions
How do I read a 4-band resistor?
First two bands are digits, third is the multiplier (power of ten), fourth is tolerance. Yellow(4), violet(7), brown(×10) = 470 Ω.
What is the difference between 4-band and 5-band resistors?
5-band resistors carry one extra digit (three significant figures instead of two) and usually tighter tolerances (1% or better) — precision parts. The reading logic is identical, shifted by one band.
What do gold and silver bands mean?
As tolerance: gold ±5%, silver ±10%. As multiplier bands: gold ×0.1, silver ×0.01 (for values under 10 Ω and under 1 Ω respectively).
Which end do I start reading from?
The end opposite the tolerance band. The tolerance band is typically gold/silver, separated by a slightly larger gap. If both ends look plausible, the reading that yields a standard E-series value (…220, 470, 680…) is usually the right way round.
What if there are only 3 bands?
Digit, digit, multiplier — with an implicit ±20% tolerance (the “no band” option in the calculator). Common in cheap, non-critical applications.
Is this resistor color code calculator free?
Yes — free, instant, no sign-up.