Resistor Color Code Calculator

This resistor colour code calculator decodes the painted bands on a through-hole resistor into its resistance value, tolerance, and the guaranteed minimum and maximum values you can expect from the part. Pick the colour of each band from the dropdowns and the resistance appears instantly, with the maths shown step by step. It is built for electronics students, hobbyists populating a breadboard, repair technicians identifying an unmarked part, and anyone who has ever squinted at a tiny component and wondered whether that third band is red or orange. Because resistors are rarely printed with their numeric value, the colour code is the universal language that lets you read a resistor at a glance.

The scheme was standardised by the international standard IEC 60062. Each colour maps to a digit, a multiplier, or a tolerance. A standard 4-bandresistor — the most common type — uses the first two bands as significant digits, the third as a power-of-ten multiplier, and the fourth as the tolerance.

Reading Color Bands

Read from left to right. The first two bands give the significant digits, the third band is the multiplier (×10ⁿ), and the fourth band is the tolerance (accuracy of the value).

Memory aid: Black Brown Red Orange Yellow Green Blue Violet Gray White = 0 1 2 3 4 5 6 7 8 9

The formula the calculator applies is: resistance = (digit₁ × 10 + digit₂) × multiplier. The multiplier band uses the same colour-to-digit map as a power of ten, so brown means ×10, red means ×100, orange means ×1,000 (1 kΩ steps), and so on. Two extra multiplier colours have no digit meaning: gold divides by ten (×0.1) and silverdivides by a hundred (×0.01), which is how sub-ohm values are encoded.

Tolerance and what it means

The tolerance band states how far the real resistance may stray from the nominal value. Gold = ±5% and silver = ±10% are by far the most common; brown is ±1%, red ±2%, and a missing fourth band means ±20%. Tolerance matters because a resistor is a manufactured part, not a perfect one. The calculator turns the percentage into a concrete range so you know the worst case for your circuit.

Worked example

Take the bands brown, black, red, gold. Brown = 1 and black = 0 give the significant digits "10". The red multiplier is ×100, so resistance = 10 × 100 = 1,000 Ω = 1.0 kΩ. The gold band means ±5%, so the true value lies between 950 Ω and 1,050 Ω. That is the default shown above — change any band to decode a different part.

E-series standard values

Resistors are not made in every conceivable value. Instead they follow logarithmic E-series sets so that, allowing for tolerance, every possible requirement is covered with the fewest parts. E12 (±10%) has 12 values per decade — 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 — while E24(±5%) has 24, and E96 (±1%) has 96 for precision work. When a calculation calls for an odd value such as 1,037 Ω, you pick the nearest E-series value (1 kΩ) or combine two resistors in series or parallel.

Tips and common mistakes

Tip: orient the resistor with the tolerance band (usually gold or silver, and often spaced slightly apart) on the right before you read. Tip: confirm a decoded value with a multimeter when in doubt — heat or age can shift a resistor outside its band. Common mistake: reading the bands backwards, which turns a 100 Ω part into something wildly different. Common mistake: confusing brown (digit 1) with red (digit 2) or orange under poor lighting — these are the classic mix-ups, so check under daylight. Common mistake: assuming a 5-band part can be read with this 4-band tool; a 5-band resistor uses three digit bands plus a multiplier and tolerance, giving tighter precision, and must be read accordingly.