Resistor Color Code Calculator
Decode a resistor's color bands into its resistance and tolerance, go the other way and turn a resistance value into the exact bands that represent it, or decode the printed numeric code on a tiny surface-mount (SMD) chip resistor. Supports 4-band, 5-band, and 6-band (with temperature coefficient) leaded resistors, plus 3-digit, 4-digit, and "R"-notation SMD codes.
Background
Resistors are too small to print numbers on reliably, so manufacturers use colored bands (or, on tiny surface-mount parts, printed digit codes) instead. Each color or digit stands for a digit, a multiplier, a tolerance, or (on precision resistors) a temperature coefficient. Reading them is just decoding a simple lookup table — but doing it by hand is easy to get wrong, especially with 5- and 6-band resistors or SMD codes. This calculator decodes bands or codes into a resistance value, or works backward from a resistance value to the color bands that represent it.
How to use this calculator
- Choose Decode Colors → Resistance if you're looking at a real leaded resistor and need its value: pick the band count, then click the color swatches to match what you see.
- Choose Encode Resistance → Colors if you know the value you need and want the bands to look for (or draw for a schematic).
- Choose SMD Numeric Code if your component is a tiny surface-mount chip resistor printed with digits (and sometimes the letter "R") instead of color bands.
- In decode mode, read bands left to right starting from the end furthest from the tolerance band — the tolerance band (usually gold or silver) is always last.
- Click Calculate to see the diagram, the full step-by-step math, and a callout explaining what the result actually means.
How resistor codes work
Each color stands for a digit 0–9: black=0, brown=1, red=2, orange=3, yellow=4, green=5, blue=6, violet=7, gray=8, white=9. The first two (4-band) or three (5-/6-band) bands spell out the significant digits.
The next band is the multiplier: it tells you how many zeros to add, or (for gold/silver) to divide by 10 or 100. Resistance = digits × multiplier.
The tolerance band tells you how far a real resistor is allowed to drift from its printed value — gold (±5%) and silver (±10%) are common on cheap resistors; brown, red, green, blue, violet, and gray get progressively tighter.
5-band resistors use a third digit for one extra significant figure of precision before the multiplier and tolerance bands.
6-band resistors add a final temperature coefficient band, measured in ppm/K (parts per million per degree Kelvin) — it tells you how much the resistance drifts as the resistor heats up, which matters for precision circuits but is negligible for most everyday use.
Going the other direction (encoding), a resistance value has to be rounded to however many significant digits the band count allows — a 4-band resistor can only represent 2 significant figures, so 999,999Ω and 1,000,000Ω end up looking identical on the bands.
Surface-mount (SMD) resistors are too small for painted bands, so the same digits-times-multiplier idea gets printed as plain numbers instead: a 3-digit code uses its last digit as the power-of-10 multiplier, and a tighter-tolerance 4-digit code works the same way with one extra significant digit.
A letter "R" inside an SMD code marks exactly where the decimal point goes and skips the multiplier entirely — "4R7" means 4.7Ω, not "4 times R times 7."
Not every digit combination corresponds to a resistor manufacturers actually stock. Common parts follow preferred-value series like E24 (24 values per decade, roughly 5% spacing) — a value can be perfectly representable on the bands and still not be something you can buy off the shelf.
Formulas & Equations Used
4-band resistance: R = (d₁d₂) × multiplier
5-/6-band resistance: R = (d₁d₂d₃) × multiplier
Tolerance range: R_min = R × (1 − tol%), R_max = R × (1 + tol%)
Encoding (rounding to n significant figures): mantissa = round(R ÷ 10^(exp−n+1)), R_reconstructed = mantissa × 10^(exp−n+1)
SMD 3-/4-digit code: R = (significant digits) × 10^(last digit)
SMD "R" notation: R replaces the decimal point directly in ohms (e.g. 4R7 = 4.7 Ω)
Example Problems & Step-by-Step Solutions
Example 1 — The classic LED resistor
A 4-band resistor reads red-red-brown-gold.
Step: Digits: red=2, red=2 → "22". Multiplier: brown=×10. R = 22 × 10.
Result: R = 220Ω, ±5% (209Ω–231Ω) — the resistor found in nearly every beginner LED circuit.
Example 2 — A 5-band precision resistor
A 5-band resistor reads brown-black-black-red-brown.
Step: Digits: 1,0,0 → "100". Multiplier: red=×100. R = 100 × 100.
Result: R = 10,000Ω (10 kΩ), ±1% — the extra digit gives one more significant figure than a 4-band resistor could.
Example 3 — Reading a temperature coefficient
The same resistor above, but 6-band, adds a red temperature coefficient band.
Step: Red tempco = 50 ppm/K.
Result: For every 1°C the resistor warms up, its resistance shifts by about 50 millionths of 10,000Ω — roughly 0.5Ω per °C, negligible for most circuits.
Example 4 — Encoding a round number
You need a 3.3 MΩ resistor (5-band, 3 significant figures).
Step: 3,300,000 = 330 × 10⁴. Digits 3,3,0 = orange, orange, black. Multiplier 10⁴ = yellow.
Result: Bands = orange-orange-black-yellow (+ tolerance) — an exact match, 0% rounding error.
Example 5 — The limits of precision
You need exactly 999,999Ω on a 4-band (2 significant figure) resistor.
Step: Rounding 999,999 to 2 significant figures gives mantissa 10, which lands as 1,000,000 (10 × 10⁵... — specifically 10 × 10⁵⁵⁵wait— 10 × 10⁵⁵? no: 10 × 10⁵⁵ — 10 × 10⁵.
Result: The bands show brown-black-green (1 MΩ) — off by only 0.0001%, but a real value of exactly 999,999Ω simply can't be shown on only 2 digits.
Example 6 — Tolerance range in practice
A 4.7 kΩ resistor with a gold tolerance band.
Step: Tolerance = ±5% of 4,700Ω = ±235Ω.
Result: Any individual unit off the factory line could measure anywhere from 4,465Ω to 4,935Ω and still be considered "good" — that's normal, not a defect.
Example 7 — Reading an SMD numeric code
A tiny chip resistor is printed with 104. A tighter 1%-tolerance part nearby reads 4992.
Step: 104 → 10 × 10⁴ = 100,000Ω. 4992 → 499 × 10² = 49,900Ω.
Result: 100 kΩ and 49.9 kΩ — the last digit is always the power-of-10 multiplier, whether the code has 3 digits or 4.
Example 8 — "R" notation and the zero-ohm jumper
One chip resistor reads 4R7. Another, oddly, reads 000.
Step: 4R7 → the R marks the decimal point → 4.7Ω. 000 → 0 × 10⁰ = 0Ω.
Result: 4.7Ω is a normal small-value part. 0Ω isn't a mistake — manufacturers print "000" on parts meant to work as a jumper wire, not limit current.
Frequently Asked Questions
How do I know which end of the resistor to start reading from?
Start from the end where the bands are spaced closer together, and read toward the widest gap. The tolerance band (usually gold or silver, occasionally brown/red/green/blue/violet) is almost always last and set apart from the rest.
What's the difference between a 4-band, 5-band, and 6-band resistor?
A 4-band resistor gives 2 significant digits of precision, a 5-band gives 3 (tighter tolerances, like ±1% or ±0.5%, need that extra digit), and a 6-band adds a temperature coefficient band on top of the 5-band format.
Why do gold and silver appear as both multiplier and tolerance colors?
They're reused for two different purposes in two different positions: as a multiplier band, gold means ×0.1 and silver means ×0.01; as a tolerance band (always the last band), gold means ±5% and silver means ±10%. Position tells you which meaning applies.
What if I can't tell two colors apart?
Lighting and color vision differences make brown/red and blue/violet especially easy to confuse. If you're not sure, a multimeter reading is the reliable fallback — use the decoded value here as a sanity check against what you measure.
Can any resistance value be represented exactly?
No. A 4-band resistor can only show 2 significant digits, and a 5-/6-band resistor only 3, so most real-world values get rounded to the nearest representable combination — the "Encode" mode shows exactly how far off that rounding is, and flags whether the result is a standard E24 stock value.
Does the temperature coefficient band matter for everyday projects?
Rarely. It typically shifts resistance by only tens of parts per million per degree — a rounding error in most hobby and classroom circuits. It matters far more in lab instruments, precision references, and temperature-sensitive analog designs.
What's the difference between color bands and SMD numeric codes?
They encode the exact same information — significant digits plus a power-of-10 multiplier — just in a different format. Surface-mount parts are too small for painted bands, so the digits and multiplier get printed directly as numbers instead of colors.
What does the letter "R" mean in a code like 4R7?
It marks exactly where the decimal point belongs and replaces the usual multiplier digit entirely. This lets manufacturers print small values like 4.7Ω without needing a negative exponent.
Is a resistor coded 000 actually broken?
No — it's intentional. A code of all zeros means 0Ω, used for surface-mount "jumper" parts that link two points on a board with the same automated placement process as every other part, instead of using a separate wire.
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