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Resistor color code calculator

Yellow, violet, orange and gold read as 47 kΩ ±5.0 %, so the part in your hand may sit anywhere between 44.65 kΩ and 49.35 kΩ and still be in spec. Read that orange ring as red and you would have picked up 4.7 kΩ - ten times too small, with the same four colors on the body.

Your circuit

Not measured yet? Leave the decoded value - the comparison then simply confirms the bands.

Result

Nominal resistance
47 kΩ
Tolerance
5.0 %
Value the part may really have
44.65 kΩ – 49.35 kΩ

If one band was read wrong

  • 4.7 kΩ · Red4.465 kΩ – 4.935 kΩthe meter says otherwise
  • 47 kΩ · Orange44.65 kΩ – 49.35 kΩmatches the meteras you read it
  • 470 kΩ · Yellow446.5 kΩ – 493.5 kΩthe meter says otherwise

Nearest catalogue value: 47 kΩ · IEC 60062, IEC 60063

How the calculation works

The code is a lookup, not a formula. Reading order is what makes it work:

digit · digit · [digit] · multiplier · tolerance · [temperature coefficient]

Two digits on a four-band part, three on a five-band one; the ring after them is the power of ten, and the ring standing apart at the far end is how far the part may legally be from the value those digits state.

Everything that goes wrong here goes wrong at the multiplier. The digits are guarded by common sense - a resistor is rarely 98 of anything - but brown, red and orange are the same ring under a warm light on an aged body, and each step between them is a factor of ten. That is why the comparison under the result is built around that ring rather than around the digits: it shows what the same four colors would mean if the multiplier were read one shade either way, with the span each reading allows, and lets the meter settle it.

The second thing worth knowing is that the bands describe the part as it left the factory. A resistor that has spent three summers next to a regulator, or one that has been reflowed twice, drifts - upwards, usually, and quietly. The code tells you what to expect; the measurement tells you what you have.

Worked example

Your circuit

Band 1 - first digit
Yellow
Band 2 - second digit
Violet
Multiplier band
Orange
Tolerance band
Gold

Result

Nominal resistance
47 kΩ
Tolerance
5.0 %
Value the part may really have
44.65 kΩ – 49.35 kΩ
Formula
R = (d₁d₂[d₃]) · 10^m · ΔR = ± t % · R
Standard
IEC 60062, IEC 60063
Limits of the model
The bands state what the part was made to, not what it is now: heat, age and a cold joint all move a resistance, which is why the meter has the last word.

Computed by Voltacalc with the same engine as the tool above.

What applies in the United States

American benches meet the code twice: on through-hole parts from the drawer, and on the 1/4 W resistors that come with hobby kits, where the bands are printed on a dark blue body that turns brown under a warm desk lamp. Anything surface-mount is numbered instead, and anything in a panel is usually a wirewound part with the value stamped on it. The practical rule in a US shop is the same as in a lab: decode the bands to know what you are looking for, then put the meter on it, because a resistor that has cooked in a poorly ventilated enclosure reads high long before it looks burnt.

Who decides
NFPA / the authority having jurisdiction (AHJ) in your state or city
Standard
NEC (NFPA 70), National Electrical Code
Ampacity table
NEC Table 310.16, with the correction and adjustment factors of 310.15(B) and (C), and the small-conductor rule in 240.4(D)
Permitted drop
The NEC does not make voltage drop a rule for most branch circuits: 210.19(A) and 215.2(A)(1) carry Informational Notes recommending no more than 3% on the branch circuit and 5% for feeder plus branch combined. Your AHJ, or a specific article such as 647.4(D), can make a lower figure mandatory. (Checked: September 12, 2026)

Questions electricians ask

Which end of the resistor do I start from?

From the end where the bands are crowded together. The tolerance band sits slightly apart from the rest, and on a four-band part it is usually gold or silver - neither of which can be a digit, so if you start from the gold end the first ring makes no sense. That is the check: if the reading is absurd, turn the part around.

Why does the calculator ask what my meter reads?

Because the bands and the meter disagree more often than people expect, and when they do it is nearly always a misread ring rather than a faulty part. The comparison under the result shows the two readings a one-color slip of the multiplier band would produce, so the measurement decides which one you are actually holding.

What does the tolerance band really buy me?

A range, not a number. A 5 % part sold as 47 kΩ is allowed to leave the factory anywhere between 44.65 kΩ and 49.35 kΩ, and that is fine in a pull-up or a bleeder. In a divider that sets a reference it is not: there you buy 1 % parts, or you measure and pair them.

Does the color code tell me the power rating?

No. Size does, roughly - a 1/4 W part is about 6 mm long, a 1 W part twice that - but nothing in the bands says how much heat the body can lose. Work the dissipation out from the current, then buy at least double.

Standards and sources

  • NEC (NFPA 70), National Electrical Code
  • NEC Table 310.16, with the correction and adjustment factors of 310.15(B) and (C), and the small-conductor rule in 240.4(D)

Last updated: September 13, 2026

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