Resistor Color Code Calculator
Work out a resistor's value from its color bands, or go the other way and find the bands for a resistance. The tolerance band is turned into a real-world range, so you can see what the part is allowed to be.
Bands read left to right from the end nearest a tolerance band (gold or silver). Reads cover the common film and carbon types; check the part marking for anything unusual.
Formula and calculation
Worked example
A four-band resistor painted brown, black, red and gold reads (10 × 1 + 0) × 100 = 1,000 Ω. The calculator reports 1,000 ohms — 1 kΩ — with a tolerance of ±5% and an acceptable range of ±5%: 950 Ω to 1.05 kΩ.
Reading the bands the right way round
Color codes run from the end where the first band sits closest to the lead, and the tolerance band is the clue: gold and silver are never digits, so a gold or silver band is the last one you read. Modern 4-band parts usually put the tolerance band on its own with a wider gap before it. Five-band parts squeeze a third digit in before the multiplier, so if you read a 5-band resistor as a 4-band one you will be out by a factor of ten.
4.7 kΩ, not 4.8 kΩ
Resistor values are not made in round numbers. The E24 series spaces 24 values across each decade — 1.0, 1.1, 1.2 and so on up to 9.1 — so that a 5% part can never be confused with its neighbour on a production line. That is why the value you design with, say 4.8 kΩ, comes back as 4.7 kΩ: it is the nearest part that exists. If the 2% gap matters, buy a 1% (E96) part instead of a 5% one.
What the results mean
- Resistance
- The resistance in ohms — decoded from the bands, or the nearest E24 standard value when you enter a target. The engineering-unit form below reads it as Ω, kΩ or MΩ.
- Minimum with tolerance
- The low end of the tolerance range: the nominal value minus its tolerance percentage. A 1 kΩ ±5% part is allowed to be as low as 950 Ω.
- Maximum with tolerance
- The high end of the tolerance range. Compare this with what your circuit actually needs — a 5% part can sit 5% off the marked value and still be within spec.
- In engineering units
- The same resistance written the way schematic and parts catalogs write it: 4.7 kΩ rather than 4,700 Ω.
- Tolerance
- The tolerance the tolerance band stands for, as a percentage. Gold is ±5%, silver ±10%, and the brown-to-gray bands cover the 1% and better precision parts.
- Acceptable range
- The full acceptable window, from minimum to maximum, so you can see whether the worst-case part still works in your circuit.
- Bands
- The bands translated back into a sentence: which band means which digit, multiplier or tolerance — the cross-check for what you read off the part.
- Against the E24 series
- How the value sits against the E24 series: an exact standard value, or how far the nearest one is. Resistors are made in the E24 steps, so real parts land on those values.
- The arithmetic
- The arithmetic with your numbers substituted, so the value can be checked by hand.
Frequently asked questions
How do I read a resistor color code?
Read the bands from the end, turn each digit band into a number, multiply by the multiplier band, and read the last band as the tolerance. Brown-black-red-gold is the classic 1 kΩ 5% part: 1, 0, then two more zeros. The calculator does the arithmetic and prints the sentence form of the bands so you can check it.
Which end do I start reading a resistor from?
Start at the end opposite the tolerance band. Gold and silver bands are tolerance or multiplier colors only — never digits — so a resistor with a gold band is read from the other end. If there is no metallic band, the tolerance band is the one set apart with a wider gap.
What is the difference between 4-band and 5-band resistors?
A 4-band code carries two significant digits and is used on 5% and 10% parts. A 5-band code carries three significant digits and is the marking on 1% and better metal-film resistors, which is how a 100 kΩ 1% part can be printed as 100 rather than 10. This calculator has a tab for each type.
Why does the value I type come back as a different resistance?
Because color codes can only express the E24 series, the 24 standard values per decade that common resistors are made in — 4.7 kΩ is one, 4.8 kΩ is not. The reverse lookup snaps to the nearest value that exists so the colors it gives you can actually be bought. If the difference matters, use a 1% (E96) part and read its printed code instead.
What do gold and silver bands mean on a resistor?
On the multiplier position, gold means ×0.1 and silver ×0.01 — they are how small values such as 0.47 Ω are written. In the tolerance position, gold is ±5% and silver ±10%. Because metallic bands are never used for digits, they also tell you which end of the part to start reading from.