# Resistor Color Code

> Decode and encode resistor bands Decode four, five or six color bands or encode an exactly representable resistance, with tolerance and temperature coefficient.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://ohmforgeresistorcolorcode.usefulweb.site/ (interactive tool at https://ohmforgeresistorcolorcode.usefulweb.site/tool)
- JSON API: POST https://ohmforgeresistorcolorcode.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://ohmforgeresistorcolorcode.usefulweb.site/api/v1/tool)
- OpenAPI: https://ohmforgeresistorcolorcode.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://ohmforgeresistorcolorcode.usefulweb.site/mcp - tool `ohmforge_resistor_color_code`

## Inputs
- mode (select): Calculate
- bandCount (select): Number of bands
- digit1 (select): First significant band (decode)
- digit2 (select): Second significant band (decode)
- digit3 (select): Third significant band (5 or 6 bands, decode)
- multiplier (select): Multiplier band (decode)
- tolerance (select): Tolerance band
- temperature (select): Temperature coefficient band (6 bands)
- ohms (number): Resistance in ohms (encode)

## Method
- Reads two significant digits for four bands and three for five or six bands, then applies the multiplier and tolerance.
- The optional sixth band is the temperature coefficient in ppm/K. Uses the conventional mappings documented in the linked Vishay chart.
- Encoding requires an exactly representable value and never silently rounds to a preferred series.
- The minimum and maximum are nominal resistance multiplied by one minus or plus tolerance; they do not include temperature effects.
- The nominal value is also checked against the IEC 60063 preferred-number series E6, E12, E24, E48, E96 and E192 (exact match of the significant digits).

## Limits
- This covers conventional four-, five- and six-band resistor markings. Manufacturers may use different markings, and color appearance or orientation can be ambiguous. Confirm against the component datasheet and measure when uncertain.