What it decodes
Select three or four bands and enter their colours in order: the first two bands are digits, the third is the multiplier, and the fourth—when present—is tolerance. Without a fourth band, the cited table assigns ±20% tolerance.
The calculator is limited to the carbon composition code table in the source. It does not attempt to identify resistor technology from appearance alone.
Band order and example
Nominal resistance is (10 × first digit + second digit) × multiplier. The table assigns black through white to digits 0–9; gold and silver multipliers are 0.1 and 0.01. A gold tolerance band means ±5%; silver means ±10%.
Red–violet–red–silver decodes to 27 × 100 = 2,700 Ω with ±10% tolerance. The nominal tolerance range is 2,430–2,970 Ω. The result is a calculated range around the nominal marking, not a measurement.
Resistance values are displayed in Ω, kΩ, MΩ or GΩ with three significant digits. Range endpoints are calculated from the unrounded nominal result.
Limits and interpretation
The source covers three- and four-band carbon composition resistors. Five-band, six-band, surface-mount, non-carbon-composition and manufacturer-specific markings are not decoded.
A printed tolerance describes the nominal component range; the calculator does not measure a resistor, account for ageing or temperature drift, or decide whether a part is suitable for a circuit.
No circuit, replacement-part, power-rating, voltage or installation decision is provided.
Common questions
What does a missing fourth band mean here?
For the three-band code in the source table, no fourth band corresponds to ±20% tolerance.
Can I decode a five-band resistor?
No. The cited material describes three- and four-band carbon composition resistors only. This calculator does not infer other code systems.
Does the tolerance range show the measured value?
No. It shows the nominal range implied by the marking. Actual resistance requires measurement with a suitable instrument.
Related tools
Source
British Columbia Industry Training Authority, Construction Electrician Apprenticeship Program, Level 1, Learning Guide D-1: Use Electrical Circuit Concepts, Version 1 (January 2011), Learning Task 11 “Resistors,” printed pages 73–74. Page 74 provides the carbon composition three-/four-band colour table and red–violet–red–silver example. This trade-learning source supports the decoding table only; no provincial code or component-selection approval is claimed.
Source and terminology checked November 10, 2026. Report a problem or suggest a source; inputs are not attached automatically.