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Resistor Color Code Calculator

Decodes the colour bands of a 4-band or 5-band resistor (IEC 60062) into its resistance, tolerance and min/max values, or encodes a resistance value into the 4-band (or 5-band) colour sequence.

Band 1 (optional)First significant digit colour (band nearest the end). Band 2 (optional)Second significant digit colour. Band 3 (5-band only) (optional)Third significant digit colour for 5-band resistors; omit for 4-band. Multiplier band (optional)Multiplier colour: black ×1, brown ×10, red ×100, orange ×1k, yellow ×10k, green ×100k, blue ×1M, violet ×10M, grey ×100M, white ×1G, gold ×0.1, silver ×0.01. Tolerance band (optional)Tolerance colour: brown ±1 %, red ±2 %, green ±0.5 %, blue ±0.25 %, violet ±0.1 %, grey ±0.05 %, gold ±5 %, silver ±10 %, none ±20 %. Resistance to encode (Ω) (optional)Give a resistance in ohms (e.g. 4700) to get its colour bands instead of decoding; band inputs are then ignored.

When to use

You need to read a resistor's bands (band colours in, ohms out) or find the bands for a given resistance value.

Do not use when: The part is an SMD resistor with a printed numeric code, a 6-band resistor (temperature coefficient band is ignored), or you need the resistor value for a circuit (use led-resistor or voltage-divider).

Formula

4-band: R = (10·d1 + d2) × multiplier; 5-band: R = (100·d1 + 10·d2 + d3) × multiplier; digits black 0 … white 9; min/max = R × (1 ∓ tolerance/100)

Inputs

Parameter	Type	Unit	Required	Description
`band1`	enum: black \| brown \| red \| orange \| yellow \| green \| blue \| violet \| grey \| white		no	First significant digit colour (band nearest the end).
`band2`	enum: black \| brown \| red \| orange \| yellow \| green \| blue \| violet \| grey \| white		no	Second significant digit colour.
`band3`	enum: black \| brown \| red \| orange \| yellow \| green \| blue \| violet \| grey \| white		no	Third significant digit colour for 5-band resistors; omit for 4-band.
`multiplier`	enum: black \| brown \| red \| orange \| yellow \| green \| blue \| violet \| grey \| white \| gold \| silver		no	Multiplier colour: black ×1, brown ×10, red ×100, orange ×1k, yellow ×10k, green ×100k, blue ×1M, violet ×10M, grey ×100M, white ×1G, gold ×0.1, silver ×0.01.
`tolerance`	enum: brown \| red \| green \| blue \| violet \| grey \| gold \| silver \| none		default gold	Tolerance colour: brown ±1 %, red ±2 %, green ±0.5 %, blue ±0.25 %, violet ±0.1 %, grey ±0.05 %, gold ±5 %, silver ±10 %, none ±20 %.
`resistance_ohm`	number	Ω	no	Give a resistance in ohms (e.g. 4700) to get its colour bands instead of decoding; band inputs are then ignored. Range: > 0, ≤ 100000000000

Outputs

Output	Type	Unit	Description
`mode`	string		'decode' (colours → value) or 'encode' (value → colours).
`resistance_ohm`	number	Ω	Nominal resistance.
`resistance_formatted`	string		Nominal resistance with SI prefix, e.g. 4.7 kΩ.
`tolerance_percent`	number	%	Tolerance from the tolerance band.
`min_resistance_ohm`	number	Ω	Nominal × (1 − tolerance).
`max_resistance_ohm`	number	Ω	Nominal × (1 + tolerance).
`band_count`	integer		4 or 5.
`band_colors`	string_list		Colours from the first digit band to the tolerance band.
`color_code`	string		The bands as a hyphen-separated string, e.g. yellow-violet-red-gold.

Example

5-band brown-black-black-red-brown: {"band1":"brown","band2":"black","band3":"black","multiplier":"red","tolerance":"brown"} → {"mode":"decode","resistance_ohm":10000,"resistance_formatted":"10 kΩ","tolerance_percent":1,"min_resistance_ohm":9900,"max_resistance_ohm":10100,"band_count":5,"color_code":"brown-black-black-red-brown"}

Encode 4.7 kΩ ±5 %: {"resistance_ohm":4700} → {"mode":"encode","band_count":4,"band_colors":["yellow","violet","red","gold"],"color_code":"yellow-violet-red-gold","min_resistance_ohm":4465,"max_resistance_ohm":4935}

GET https://tttkmbb.com/api/v1/calculate/resistor-color-code?band1=brown&band2=black&band3=black&multiplier=red&tolerance=brown

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/resistor-color-code (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/resistor-color-code · Markdown: https://tttkmbb.com/engineering/resistor-color-code.md · JSON definition: https://tttkmbb.com/engineering/resistor-color-code.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="resistor-color-code"
OpenAPI operationId: convert_resistor_color_code
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Wikipedia – Electronic color code (IEC 60062) (reference)
Digi-Key – Resistor color code calculator and reference (4, 5 and 6 bands) (reference)

FAQ

Which end do I read from?

The tolerance band (gold, silver or a band set apart by a wider gap) is last; read from the opposite end. Gold or silver can never be a first band.

Why can't a value be encoded?

Colour bands hold only 2 (4-band) or 3 (5-band) significant digits and a power-of-ten multiplier down to ×0.01. Values like 4735 Ω or 0.047 Ω have no exact code; round to a preferred (E-series) value.

Related calculators

LED Resistor Calculator — Find the resistor value you need before reading its bands.
Resistors in Series and Parallel Calculator — Combine several decoded resistors.
Ohm's Law Calculator — Use the decoded value in V = I·R.