How to Read Resistor Color Codes

What the bands mean, how to work out 4, 5 and 6-band parts, how to tell which end is band 1, and where standard values come from.

What the bands mean

Small through-hole resistors are too thin to print a number on, so the value is painted as color bands. IEC 60062 sets which color means what. The current edition is the 6th, from 2016.

Table 1 of the standard gives 13 colors a digit, a multiplier, a tolerance and a tempco. Black through white are the digits 0 to 9. Gold, silver and pink have no digit and only show up as multipliers or tolerances.

The multiplier is a power of ten: red is x100, orange is x1000. Gold is x0.1, silver x0.01 and pink x0.001, which is how values under 1 ohm get a code.

4, 5 and 6-band codes

A 4-band part is two digits, a multiplier and a tolerance. Figure 2 in the standard is violet, green, yellow, gold: 75 x 10,000 = 750 kΩ at ±5%.

A 5-band part has three digits for finer values. Figure 3 is red, yellow, white, orange, brown: 249 x 1,000 = 249 kΩ at ±1%. A 6-band part adds a tempco band after that. In Figure 4 band 6 is red, which means ±50 ppm/K.

A 3-band part has no tolerance band, and the standard says a missing fourth band means ±20%. Figure 1 is blue, gray, red: 68 x 100 = 6.8 kΩ.

What this calculator does

On the first page, pick the band count, then tap a color for each band. You get the value, the tolerance and the min to max range. Every slot offers all 13 colors, so you can enter exactly what you see even if you're holding the part backwards.

We read your sequence both ways against the IEC table. If only one way works, you get that value and the band that breaks the other way. If both work, you see both values side by side, with a note on which one is a standard value.

On the value page, type something like 4.7k and get the 2-digit and 3-digit codes. Every color is labeled with its name and two-letter code, so you can read it without telling colors apart.

Which end is band 1

Clause 3.1 of the standard says band 1 is the one nearest the end of the resistor, and the tolerance band is 1.5 to 2 times wider than the rest. So start at the end where the bands crowd the edge, and if one band is wide, keep it last.

Colors help too. Gold, silver and pink have no digit, so they can't be band 1. If a 4-band part has gold at one end, that end is the last band.

Some parts read fine both ways, like a 5-band that starts and ends with brown. Then look at band widths, or just measure it.

Standard values

Resistor values come from the E series in IEC 60063. E24 has 24 values per decade: 10, 11, 12, 13, 15 and so on. Table 3 of that standard pairs ±5% parts with E24 and ±1% parts with E96.

E12 is every second E24 value, and E6 is every second E12 value. The standard notes that E24 values 27 through 47, plus 82, differ from the formula, and were kept for historical reasons.

The value page checks your number against all four series and shows the next value below and above when it isn't one. Measuring closeness as a ratio is our rule, not the standard's.

Where people get stuck

Red and orange, brown and red, blue and violet are easy to mix up under warm light. If the result isn't in any E series, swap one look-alike color and try again, or measure it.

Charts disagree on gray tolerance. The 2016 standard says ±0.01%, while plenty of online charts say ±0.05%. This calculator follows the standard and notes the difference on the chart page.

Blue or tan resistor bodies can be mistaken for a band. Count the bands first, pick that count, then enter colors.

Sources

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