Pick the bands you can see and read off the value, the tolerance, and the range the real component is guaranteed to fall inside.
A resistor is too small to print a number on legibly, so its value is painted on as coloured rings. On a four-band part the first two bands are digits, the third is a power-of-ten multiplier, and the fourth is tolerance. A five-band part adds a third significant digit, which is how precision resistors express values a four-band code cannot reach. A six-band part adds a temperature coefficient in parts per million per degree Celsius.
The tolerance band is normally separated by a slightly wider gap, and gold or silver only ever appear as multiplier or tolerance — never as a digit. Those two facts are usually enough to work out which end to read from. If you are still unsure, read it both ways: one direction almost always produces a value that exists in the standard series and the other produces something absurd.
| Colour | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | × 1 | — |
| Brown | 1 | × 10 | ± 1% |
| Red | 2 | × 100 | ± 2% |
| Orange | 3 | × 1 k | — |
| Yellow | 4 | × 10 k | — |
| Green | 5 | × 100 k | ± 0.5% |
| Blue | 6 | × 1 M | ± 0.25% |
| Violet | 7 | × 10 M | ± 0.1% |
| Grey | 8 | × 100 M | ± 0.05% |
| White | 9 | × 1 G | — |
| Gold | — | × 0.1 | ± 5% |
| Silver | — | × 0.01 | ± 10% |
Brown, black, red, gold. Brown is 1, black is 0, giving 10. Red as a multiplier is ×100, so the value is 1000 Ω, or 1 kΩ. Gold means ±5%, so the part is guaranteed to measure somewhere between 950 Ω and 1050 Ω. Anything outside that band is a failed component, not a tolerance issue.
That range matters more than people expect. Put two 5% resistors in a voltage divider and the worst-case output error is not 5% — the two errors can compound in opposite directions. If a circuit’s behaviour depends on a precise ratio, buy 1% parts rather than hoping.
Resistors are not made in every value. They come in standard series — E12 for 10% parts, E24 for 5%, E96 for 1% — spaced logarithmically so that each value’s tolerance band just touches the next. In E24 the decade runs 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91. If you decode a band set to something like 4.4 kΩ, you have almost certainly misread a colour, because that value is not manufactured.
The awkward-looking numbers are deliberate. In a 10% series, 10 covers 9 to 11, and the next value up has to start where that stops, which lands on 12 rather than a round 15 or 20.
Bands fade, and on some body colours red and orange or brown and violet are genuinely hard to tell apart under warm light. Small surface-mount resistors skip colours entirely and use a printed three or four digit code where the last digit is the multiplier — 472 means 47 × 10² = 4.7 kΩ. If in doubt, measure it: a multimeter on the resistance range settles the question in seconds, as long as the component is out of circuit or the circuit is unpowered.
Start from the end where the bands are grouped closest together. The tolerance band normally sits alone with a wider gap before it. Gold and silver are only ever multiplier or tolerance bands, so if you see one it is at the far end from where you should start. As a sanity check, read it both directions and keep whichever gives a value that exists in the standard E-series.
It is the temperature coefficient, in parts per million per degree Celsius — how much the resistance drifts as the part heats. Brown is 100 ppm/°C, red 50, orange 15, yellow 25, blue 10, violet 5. It only matters in precision analogue work, reference circuits and instrumentation. For general use you can ignore it, which is why this calculator reports value and tolerance rather than drift.
For pull-ups, current limiting on an LED, and most digital work, comfortably. For anything where a ratio sets an output — voltage dividers, op-amp gain, feedback networks, current sense — tolerance stacking makes 1% parts worth the small extra cost. The rule of thumb is that if changing the value by 5% would change what the circuit does in a way you would notice, do not use 5% parts.
A missing fourth band means ±20%. It is an old convention and you will mostly meet it on vintage equipment; modern parts almost always carry at least a gold band. Read the three bands as digit, digit, multiplier exactly as you would otherwise.
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