Resistor Color Code Calculator

Frequently Asked Questions

How do I read a 4-band resistor?

Bands 1 and 2 are digits, band 3 is a multiplier (×10ⁿ), band 4 is tolerance. Brown, black, red, gold = 1, 0, ×100, ±5% = 1,000 Ω ±5%.

What are the digit colors?

Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Gray 8, White 9. Mnemonic: "Bad Boys Race Our Young Girls But Violet Generally Wins."

What's the difference between 4-band and 5-band?

5-band resistors have three significant digits instead of two for higher precision. The first three bands are digits, the fourth is the multiplier, the fifth is tolerance.

What does the tolerance band tell me?

How close to nominal the actual value is. Gold is ±5%, silver ±10%, brown ±1%, red ±2%. A 100 Ω ±5% resistor measures 95-105 Ω.

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How This Calculator Works

Resistors encode their value in coloured bands rather than printed numbers, because the parts are too small to label and the rings stay readable from any angle. Select whether your resistor has 4 or 5 bands, then pick each band's colour from the dropdowns. This tool reads the first bands as significant digits, applies the multiplier band as a power of ten, and uses the final band as the tolerance, returning the nominal resistance in ohms (auto-scaled to kΩ, MΩ or GΩ) plus the minimum and maximum the part is guaranteed to fall within. A 4-band resistor uses two digit bands; a 5-band adds a third digit for one more figure of precision.

Formula / Method

For a 4-band resistor: resistance = (digit₁ × 10 + digit₂) × multiplier. For a 5-band: resistance = (digit₁ × 100 + digit₂ × 10 + digit₃) × multiplier. Digit colours map Black = 0 through White = 9. The multiplier band is a power of ten by the same colour scheme (Red = ×100, Orange = ×1,000), with Gold = ×0.1 and Silver = ×0.01 for small values. The tolerance band gives the percentage spread: min = resistance × (1 − tol %) and max = resistance × (1 + tol %). Common tolerances: Gold ±5%, Silver ±10%, Brown ±1%, Red ±2%, Green ±0.5%, Blue ±0.25%; no band means ±20%.

Worked Example

A 4-band resistor reads Red, Violet, Orange, Gold. Digits: Red = 2, Violet = 7, so the two-digit number is 27. Multiplier Orange = ×1,000, giving 27 × 1,000 = 27,000 Ω = 27 kΩ. Gold tolerance is ±5%, so the part is guaranteed between 25,650 Ω and 28,350 Ω. A 5-band example, Brown, Green, Black, Red, Brown: digits 1, 5, 0 form 150; multiplier Red = ×100, so 150 × 100 = 15,000 Ω = 15 kΩ at ±1% (Brown), ranging 14,850 Ω to 15,150 Ω.

Common Mistakes

Reading the bands backwards - the tolerance band (often gold or silver, and slightly separated) goes last; start from the opposite end.

Confusing the multiplier with a digit - in a 4-band part the third band is the power-of-ten multiplier, not a third significant figure.

Mixing up similar colours - brown, red and orange look alike under poor light; check against a known resistor or a meter.

Forgetting Gold and Silver act as fractional multipliers (×0.1, ×0.01) for sub-10 Ω values, not just as tolerances.

Assuming the nominal value is exact - the tolerance band defines the real guaranteed range, which matters in precision circuits.

Tips & FAQ

How do I remember the digit order? A classic mnemonic for Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White (0-9) is "Big Brown Rabbits Often Yield Great Big Violet Gray Wishes." Why use 5 bands? The extra digit band gives a third significant figure and usually a tighter tolerance (1% or better), so 5-band resistors are standard in precision circuits. What about the power rating? Colour bands encode resistance and tolerance only, not wattage; resistors are separately rated (¼W, ½W, 1W and up), and since dissipated heat equals I²R, exceeding the rating burns the part out. Why do real resistors come in odd values like 4.7 kΩ? They follow standardised E-series (E12, E24, E96) chosen so the tolerance bands of adjacent values just overlap, covering the whole range with the fewest parts. Why auto-scale the units? Showing 27 kΩ instead of 27,000 Ω matches how schematics and datasheets label values, reducing transcription errors.

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