Resistor Color Code Calculator

How the resistor color code works

Through-hole resistors are too small to print a number on, so the value is painted on as rings of color defined by IEC 60062. On a four-band part the first two bands are significant digits, the third is a power-of-ten multiplier, and the fourth — set slightly apart from the rest — is the tolerance. A five-band part inserts a third significant digit before the multiplier, which is how precision resistors express values that two digits cannot reach. The digits run in spectrum order: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. Gold and silver never appear as digits; they only ever mean a fractional multiplier or a loose tolerance.

Worked example: yellow, violet, red, gold

This is the resistor sitting in every hobby kit. Yellow is 4 and violet is 7, giving 47. Red as the multiplier means x100, so 47 x 100 = 4,700 ohms, written 4.7 kΩ. Gold is ±5%, which is 235 ohms either side, so any part that measures between 4,465 Ω and 4,935 Ω is in spec. If your meter reads 4.63 kΩ, the resistor is fine — that is normal spread, not a fault.

Worked example: a five-band 4.99 kΩ

Yellow, white, white, brown, brown decodes as 4, 9, 9 then x10, giving 4,990 Ω with a brown ±1% tolerance band. The in-spec window is 4,940 to 5,040 ohms. Notice that this is the closest a real catalogue part gets to a round 5 kΩ, and it exists only because the fifth band buys a third digit. Miscounting the bands is the classic mistake here: read the same part as four bands and yellow-white-white-brown becomes 49 x 1G, which is nonsense, and that absurd answer is your clue to recount.

Small values: the gold and silver multipliers

Brown, black, gold, gold is 10 x 0.1 = 1 Ω ±5%. Silver as a multiplier means x0.01, so brown-black-silver is 0.1 Ω. These sub-ohm parts are current-sense and inrush-limiting resistors, and they are worth double-checking because a gold band at the wrong end turns a 1 Ω part into a 1 MΩ reading.

Remembering the order

The old shop-floor mnemonic for the color order is offensive and best forgotten. A clean one that maps to the same sequence is "Better Be Right Or Your Great Big Values Go Wrong": Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey, White — 0 through 9 in order. The multiplier column follows the same list, each color adding one more zero, and gold and silver hang off the bottom as x0.1 and x0.01.

Verify with a multimeter

Color reading is a guess until a meter agrees with it. Set a digital multimeter to resistance, touch the probes together first to see the lead resistance (typically 0.2 to 0.5 Ω) and subtract that from low readings. Measure the resistor out of circuit whenever you can: anything in parallel on the board — another resistor, a coil, a semiconductor junction — will pull the reading low and make a good part look faulty. Under fluorescent light, brown, red and orange are genuinely hard to separate, and grey against silver is worse; a phone torch at an angle, or simply reading the part against a white sheet, resolves most of it.

What about SMD resistors?

Surface-mount chips carry no color bands, so the same values arrive as printed codes. A three-digit code is two digits plus a zero count: 472 is 47 followed by two zeros, or 4.7 kΩ. A four-digit code on precision parts is three digits plus a count: 4702 is 470 followed by two zeros, 47 kΩ. An R marks the decimal point, so 4R7 is 4.7 Ω. The tightest 1% parts use EIA-96, a two-digit lookup code plus a letter multiplier, where 01C means 100 x 100 = 10 kΩ. And a plain 0 or 000 is a zero-ohm link — a jumper wearing a resistor body, which the color code writes as a single black band.