Index / Units
Resistor Colour Code
Three, four, five or six bands into a resistance, and a resistance back into bands. The tolerance range is worked out exactly, and the value is checked against the preferred-value series it is supposed to come from.
Reading
4700, 4.7k, 4k7, 0.22, 220R, 1M2 and 2200Ω are
all read. An empty box is zero ohms, which has no bands.
Resistance
--
Lowest in tolerance
--
Highest in tolerance
--
Band by band
The same value, written the other ways
exactPreferred values
The tables used, and where they disagree with the formula
The digit and multiplier colours are IEC 60062, and they are the
part everybody agrees on: black 0 through white 9, with the multiplier
band the power of ten. Gold and silver as multipliers mean
×0.1 and ×0.01, which is how a resistor below 10 Ω is
marked.
Tolerance: brown ±1%, red ±2%, green ±0.5%, blue ±0.25%, violet ±0.1%, grey ±0.05%, gold ±5%, silver ±10%. A resistor with no tolerance band is ±20%, which is why a three-band part is shown here as ±20% rather than as having no tolerance at all.
The sixth band is the least standardised thing on the part. The values used here are black 250, brown 100, red 50, orange 15, yellow 25, green 20, blue 10, violet 5 and grey 1 ppm/K. Some manufacturers use the sixth band for a failure rate instead, and a few use it for a reliability grade; if the datasheet says something else, the datasheet is right.
The arithmetic is exact. The value is held as a digit string and a power of ten, never as a floating-point number, so 47 × 0.01 is 0.47 here rather than 0.47000000000000003. The tolerance bounds are integer multiplications by (10,000 ± the tolerance in hundredths of a percent), with the decimal point moved afterwards.
E6, E12 and E24 are shipped as the published tables. They are not the formula: 1010/24 is 2.610, and E24 lists 2.7. Seven of the 24 entries deviate from a rounded 10k/24, and they are marked below when one comes up. E48, E96 and E192 are generated from 10k/n rounded to three significant figures, which is what those series are defined to be.
Nearest preferred value is chosen by ratio, not by difference. A series is geometric, so the nearest value to 3.0 in E12 is the one with the smallest |ln(value/3.0)|, which is 2.7 rather than 3.3 — the opposite of what subtracting gives.
Bands are read from the end that has them crowded together. If a resistor is read backwards the colours still make a number, and it is usually the wrong one; the only defence is that the tolerance band is gold or silver often enough to give the direction away.
Tolerance: brown ±1%, red ±2%, green ±0.5%, blue ±0.25%, violet ±0.1%, grey ±0.05%, gold ±5%, silver ±10%. A resistor with no tolerance band is ±20%, which is why a three-band part is shown here as ±20% rather than as having no tolerance at all.
The sixth band is the least standardised thing on the part. The values used here are black 250, brown 100, red 50, orange 15, yellow 25, green 20, blue 10, violet 5 and grey 1 ppm/K. Some manufacturers use the sixth band for a failure rate instead, and a few use it for a reliability grade; if the datasheet says something else, the datasheet is right.
The arithmetic is exact. The value is held as a digit string and a power of ten, never as a floating-point number, so 47 × 0.01 is 0.47 here rather than 0.47000000000000003. The tolerance bounds are integer multiplications by (10,000 ± the tolerance in hundredths of a percent), with the decimal point moved afterwards.
E6, E12 and E24 are shipped as the published tables. They are not the formula: 1010/24 is 2.610, and E24 lists 2.7. Seven of the 24 entries deviate from a rounded 10k/24, and they are marked below when one comes up. E48, E96 and E192 are generated from 10k/n rounded to three significant figures, which is what those series are defined to be.
Nearest preferred value is chosen by ratio, not by difference. A series is geometric, so the nearest value to 3.0 in E12 is the one with the smallest |ln(value/3.0)|, which is 2.7 rather than 3.3 — the opposite of what subtracting gives.
Bands are read from the end that has them crowded together. If a resistor is read backwards the colours still make a number, and it is usually the wrong one; the only defence is that the tolerance band is gold or silver often enough to give the direction away.