Enrichment · STEM Explorations · Electronics

Colour bands in,
ohms and tolerance out.

Pick the colours you see. The calculator gives the resistance, the range its tolerance allows and whether your multimeter reading is inside it, and it catches a resistor read back to front.

Read the bandsWhat you get

The resistor tolerance calculator

The worked example is a 4.7 kΩ, 5% resistor that measured 4.62 kΩ on a multimeter. Nothing you type leaves this browser.

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What you get

Enrichment · STEM ExplorationsFree

What you finish with
Nominal resistance, the tolerance range, an in-or-out check for a measured value with its percent difference, the E-series check and a band-by-band reading. It prints as a summary and downloads as a spreadsheet.
Who it is for
Electronics and robotics students, STEM clubs and makerspaces, and teachers running circuit labs.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The STEM Explorations space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Hold the resistor with the tolerance band on the right.
  2. Choose 4 or 5 bands.
  3. Pick each colour from left to right.
  4. Type the multimeter reading if you have one.
  5. Read the value and whether it is in tolerance.

Read the bands

How the code works

Digits, zeros and a margin.

The worked example: a 4.7 kΩ resistorYellow, violet47digits 4 and 7Red multiplier4,700 Ω47 × 100Gold, ± 5%± 235 Ω4,465 to 4,935 ΩMeasured4.62 kΩ-1.70%, in toleranceThe worked example: a 4.7 kΩ resistorYellow, violet47digits 4 and 7Red multiplier4,700 Ω47 × 100Gold, ± 5%± 235 Ω4,465 to 4,935 ΩMeasured4.62 kΩ-1.70%, in tolerance
The first bands are digits, the next is how many zeros to add, and the last says how far the real part may stray from that value.

Reading the bands

On a 4-band resistor the first two bands are digits and the third is the multiplier, the number of zeros: yellow (4), violet (7), red (× 100) is 4,700 Ω, written 4.7 kΩ. Five-band resistors use three digits for finer values. Gold and silver in the multiplier position divide by 10 and 100. The last band is the tolerance; gold is ±5%, brown ±1%.

Tolerance and standard values

Tolerance is how far a real part may differ from its marked value: a 4.7 kΩ ±5% resistor can be anything from 4,465 to 4,935 Ω and still be good. That is why values come in series such as E12 and E24, spaced so each tolerance band touches the next. Measure out of circuit, because other components in parallel change the reading.

Sources

  1. International Electrotechnical Commission. IEC 60062: Marking codes for resistors and capacitors (iec.ch).
  2. International Electrotechnical Commission. IEC 60063: Preferred number series for resistors and capacitors (E series) (iec.ch).
  3. Horowitz, P., and Hill, W. (2015). The Art of Electronics (3rd ed.). Cambridge University Press: appendix on resistor types and values.
  4. OpenStax. College Physics 2e (2022), chapter 21: resistors in series and parallel (openstax.org).

The worked example is made up. Colours can be hard to tell apart under poor light; a multimeter settles it. Your entries stay in this browser. Support: team@caveatacademic.com.