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Resistor Calculator | Decode Colour Bands and Combine Values

Quick reference

Resistor color values:

Color	Digit	Multiplier
Black	0	x1
Brown	1	x10
Red	2	x100
Orange	3	x1k
Yellow	4	x10k
Green	5	x100k

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Responsive design tested down to a 320px-wide phone screen. The input fields use native number/date keyboards on iOS and Android, the calculate button is thumb-sized, and the result still reads big and bold on the smallest screen. No app to download, ever.

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Interpretation guide

Tolerance bands:

Color	Tolerance
Gold	+/-5%
Silver	+/-10%
Brown	+/-1%
Red	+/-2%

lightbulb Worked example — reading yellow-violet-red-gold

A resistor's bands read yellow, violet, red, gold. Yellow = 4, violet = 7, red = ×100 multiplier, gold = ±5% tolerance. Resistance = 47 × 100 Ω.

Result: 4,700 Ω = 4.7 kΩ, tolerance ±5% → acceptable range 4,465–4,935 Ω.

What this means: For a 5 V circuit needing about 1 mA through an LED branch, 4.7 kΩ gives roughly 1.06 mA — close enough given the ±5% tolerance. If the design needs tighter control, pick a brown-band (±1%) part instead.

Formula & methodology

Formula: 4-band: digit, digit, x multiplier, tolerance; 5-band adds a third significant digit

How resistance is decoded

Each color maps to a digit (black = 0 through white = 9). On a 4-band resistor the first two bands are significant digits, the third is a power-of-ten multiplier, and the fourth is tolerance; 5-band parts add a third significant digit for precision.

Value: digits × multiplier — e.g. yellow-violet-red = 47 × 100 = 4,700 Ω.
Tolerance: gold ±5%, silver ±10%, brown ±1%, red ±2%.
Networks: series adds directly (R₁ + R₂); parallel combines as 1/R = 1/R₁ + 1/R₂.

Read with the tolerance band on the right so the digit bands come first, left to right.

Authoritative source: timeanddate.com

Frequently asked questions

How do I read a 4-band resistor?

Enter the required values into the input fields and press the calculate button. The tool applies the formula 4-band: digit, digit, x multiplier, tolerance; 5-band adds a third significant digit and returns the result with a short explanation of each step, so you can check the working yourself.

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

The Resistor Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Decodes resistor colour bands into resistance values, and solves series and parallel resistor networks. Enter the four or five colour bands and the tool returns the resistance, tolerance, and temperature coefficient. You can also enter resistor values to find There is no limit on usage, and it works on any device.

What does the gold band mean?

The Resistor Calculator is a free online tool that decodes resistor colour bands into resistance values, and solves series and parallel resistor networks. enter the four or five colour bands and the tool returns the resistance, tolerance, and temperature coefficient. you can also enter resistor values to find. You enter a few values, and it returns an accurate result together with a step-by-step explanation, so it works as both a calculator and a quick reference for the underlying concept.

How do I read the bands in the right direction?

Hold the resistor so the tolerance band (gold, silver, or none) is on the RIGHT. Read the first two or three significant digits left to right, then the multiplier, then the tolerance. The calculator does this automatically when you select the band colors — it also handles the direction ambiguity by checking which reading is plausible.

Can I find the color code from a resistance value?

Yes — enter a resistance value like 4,700 Ω and the calculator returns the band colors (yellow, violet, red for a 4-band 4.7 kΩ, or a 5-band code for more precision). It also shows the E-series value it matches and the tolerance options, so you can identify the physical resistor you need on the shelf.

Does it also combine resistors in series and parallel?

Yes. Enter two or more values and pick series (they just add: R1 + R2) or parallel (1/R = 1/R1 + 1/R2). Two 100 Ω resistors in parallel give 50 Ω; in series they give 200 Ω. Handy when you don't have the exact value in your parts box.

What does the multiplier band actually do?

It sets the power of ten you multiply the digit bands by. Red means ×100, so digit bands reading 47 become 4,700 Ω. Gold and silver multipliers mean ×0.1 and ×0.01 — that is how sub-10 Ω resistors are coded.

Is my data sent anywhere when I calculate?

No — decoding happens on the page itself, so nothing you enter leaves your device.

How precise is the decoded value?

The decoded resistance is exact per the color code standard, but the physical resistor varies within its tolerance band — ±5% for gold, ±1% for brown. A 4.7 kΩ gold-band resistor can legitimately measure anywhere from 4,465 to 4,935 Ω.

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