What this calculator does
Read the colored stripes on a resistor to find its value, or find the stripes to look for when you need a certain value. Small resistors with wire legs (through-hole resistors) are too tiny to print a number on. So their value is painted on as colored bands. Each color stands for a digit from 0 to 9. A later band says how many zeros follow, and another gives the tolerance (how far off the real value may be). On precision parts, a sixth band gives the temperature coefficient: how much the value drifts with heat.
This resistor color code calculator works both ways. Choose the colors you see to get the resistance, written with the usual kΩ (thousand ohms) or MΩ (million ohms). You'll also see the range the tolerance allows. Or enter a resistance to get the bands to look for. It follows the international color code in IEC 60062, which is used on resistors worldwide.
Where it's used
Why this math matters outside the classroom:
- Electronics kits. Hobbyists read yellow, violet, red as 47 × 100 = 4,700 Ω before soldering a part into a circuit board.
- Powers of ten. Students see that each step up the multiplier colors, from brown ×10 to red ×100, adds one more zero to the value.
- Checking tolerance. A technician accepts a 4.7 kΩ ±5% resistor that measures 4,610 Ω because it falls between 4,465 and 4,935 Ω.
- Repair work. A repairer replacing a burnt 220 Ω resistor looks for the bands red, red, brown on a replacement part.
- Lab benches. Physics students sort a mixed bag of resistors by color code before building an Ohm's law experiment.
Grade level and standards: Grades 5–6; Common Core State Standards for Mathematics 5.NBT.A.2, 6.RP.A.3.c. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Choose the direction: colors to resistance, or resistance to colors.
- Choose 4, 5 or 6 bands. Four-band resistors have two digit bands; five- and six-band precision resistors have three.
- To decode, pick each band's color. Start from the end farthest from the gap, or from the gold or silver band. To encode, enter the resistance and choose the tolerance.
- Read the value, its minimum and maximum, and the temperature coefficient for 6-band parts.
What the inputs mean
- Number of bands
- Count the bands. If there's a wider gap before the last band, read from the other end. Gold and silver are never the first band, which helps you find the starting end.
- Multiplier band
- The multiplier is a power of ten: black ×1, brown ×10, red ×100, up to white ×1,000,000,000. For values under 10 Ω, gold divides by 10 and silver by 100.
- Tolerance band
- Gold (±5%) and silver (±10%) are common on 4-band resistors. Brown (±1%) and red (±2%) are common on precision parts. No band at all means ±20%.
- Resistance
- A 4-band code can show 2 significant digits (the digits that carry the value), and a 5- or 6-band code can show 3. So values such as 4.75 kΩ need 5 bands.
Formula and method
resistance = (digit bands as a number) × 10^multiplier 4 bands: R = (10·d₁ + d₂) × 10^m 5 or 6 bands: R = (100·d₁ + 10·d₂ + d₃) × 10^m range = R × (1 − tolerance) to R × (1 + tolerance) digits: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; gold ×0.1, silver ×0.01
Here's what the letters mean. R is the resistance in ohms (Ω). d₁, d₂ and d₃ are the digits from the first, second and third bands. m is the multiplier band's digit, which is how many zeros to add.
The digit bands make a two- or three-digit whole number. The multiplier band then moves the decimal point by its digit. Encoding runs the same rule backward. The resistance is written as a whole number of the right length times a power of ten. Then each part is turned into its color.
Tolerance is how far the maker allows the real value to stray from the rated (nominal) value. The temperature coefficient is measured in parts per million per kelvin (ppm/K, where 1 kelvin is a 1 °C change). It says how much the resistance drifts as the part warms up.
Worked example
A 4-band resistor reads yellow, violet, red, gold.
- Yellow is 4 and violet is 7, so the digits read 47.
- Red is the multiplier 10², so 47 × 100 = 4,700 Ω.
- Gold is ±5%: 4,700 × 0.95 = 4,465 Ω and 4,700 × 1.05 = 4,935 Ω.
Result: The resistor is 4.7 kΩ ±5%, so a good part measures between 4,465 Ω and 4,935 Ω.
Understanding the result
If your meter reading falls inside the range, the part is within its tolerance. Measure resistors out of the circuit, because other parts connected alongside them change the reading.
Most resistors come in standard sets of preferred values, such as 10, 22, 47 and 68 in each power of ten. If a value you decode looks unusual, you may be reading the bands from the wrong end.
Assumptions and limitations
- Bands follow the IEC 60062 color code. They're read from the end where a band sits nearest the edge.
- Colors have been identified correctly. Brown, red and orange can be hard to tell apart on old parts.
- Surface-mount resistors (tiny flat ones soldered onto the board) use printed number codes instead of colors, and aren't covered.
- Grey tolerance is shown as ±0.01%, as in the current standard. Some older charts list ±0.05%.
- A few makers use their own schemes, such as a single black band for a zero-ohm link.
Frequently asked questions
Which end of the resistor do I start reading from?
Start from the end where the bands are closest to the edge. The tolerance band is often set apart by a wider gap. Gold or silver never show up as the first digit. So if one end shows gold or silver, start from the other end.
What is the difference between 4-band and 5-band resistors?
A 5-band resistor has a third digit band. So it can show values with three significant digits, such as 4.75 kΩ. These are usually precision parts, with a tolerance of 1% or tighter.
What does the sixth band mean?
It's the temperature coefficient, in ppm/K. A brown band means 100 ppm/K. That means a 10 kΩ resistor drifts by about 1 Ω for each degree it warms.
Why does the calculator say my value can't be shown with 4 bands?
Two digit bands can only hold two significant digits. 4.7 kΩ works, but 4.75 kΩ needs a third digit. So it's only made as a 5- or 6-band resistor.
How this calculator is checked
Method: IEC 60062:2016 resistor color code: digit, multiplier, tolerance and temperature-coefficient bands. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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