How to Read Resistor Color Codes (4-Band and 5-Band): The Chart, Two Worked Examples, Tolerance, and the Ohm's Law Check on iPhone

A resistor the size of a grain of rice carries its value as three, four or five painted stripes, and every electrician, apprentice and electronics hobbyist eventually stands at a bench squinting at one, unsure whether that band is red or brown and which end is the start. The resistor color code is a fixed table, it has not changed in decades, and it takes about ten minutes to learn properly. This post is that ten minutes: the chart, how four- and five-band resistors differ, how to work out which way round to read, two worked examples, the mistakes that produce a value ten times out, and then how to check the answer with the resistor code and Ohm's law tools in Electrician Calculator Toolkit on an iPhone.

The color chart

Ten colors stand for the digits zero to nine. The same colors double as the multiplier (the number of zeros to add, or the power of ten), and a shorter list stands for the tolerance. Here is the whole table in one place.

• Black 0, multiplier ×1
• Brown 1, multiplier ×10, tolerance ±1%
• Red 2, multiplier ×100, tolerance ±2%
• Orange 3, multiplier ×1,000
• Yellow 4, multiplier ×10,000
• Green 5, multiplier ×100,000, tolerance ±0.5%
• Blue 6, multiplier ×1,000,000, tolerance ±0.25%
• Violet 7, multiplier ×10,000,000, tolerance ±0.1%
• Grey 8, tolerance ±0.05%
• White 9
• Gold multiplier ×0.1, tolerance ±5%
• Silver multiplier ×0.01, tolerance ±10%
• No band tolerance ±20%

The digit order is the one most people learn with a mnemonic. Any mnemonic works; what matters is that black is zero and white is nine, and that gold and silver never appear as digits, only as a multiplier or a tolerance. That last fact is the key to reading direction.

Four bands: two digits, a multiplier, a tolerance

On a standard four-band resistor the first two bands are significant digits, the third is the multiplier and the fourth is the tolerance. Read the two digits as a two-digit number, then multiply by the third band.

Worked example 1: brown, black, red, gold. Brown is 1, black is 0, so the digits are 10. Red as a multiplier is ×100, so 10 × 100 = 1,000 Ω, which is 1 kΩ. Gold is ±5%, so the real value sits between 950 Ω and 1,050 Ω. This is one of the most common resistors in existence, which makes it a good one to memorise as a sanity check for the method.

The multiplier is the band that trips people up. Red as a digit is 2, but red as the third band is 'add two zeros'. Orange adds three zeros (so yellow-violet-orange is 47,000 Ω, or 47 kΩ), and black as a multiplier adds none (red-red-black is 22 Ω). Gold and silver as multipliers divide: red-red-gold is 2.2 Ω.

Five bands: three digits, a multiplier, a tolerance

Precision resistors, typically ±1% and tighter, need three significant digits, so they carry five bands: three digits, a multiplier, a tolerance. The chart is the same; only the position of the multiplier moves.

Worked example 2: red, red, black, black, brown. Red 2, red 2, black 0 give the digits 220. Black as the fourth band is ×1, so the value is 220 Ω. Brown as the fifth band is ±1%, so the resistor is between 217.8 Ω and 222.2 Ω. Compare that with the four-band version of the same value, red-red-brown-gold (22 × 10 = 220 Ω, ±5%): same nominal value, different precision, different number of stripes.

Six-band resistors exist too; the sixth band is a temperature coefficient (brown 100 ppm/K, red 50, orange 15, yellow 25). You can read the value exactly as for five bands and ignore the sixth unless the design depends on drift with temperature.

Which end do you read from?

The code has no arrow, so three clues decide the direction.

• The tolerance band is usually spaced further from the others. Hold the resistor so the lonely band is on the right and read left to right.
• Gold and silver are never first. If one end has a gold or silver band, that is the tolerance end. On a four-band resistor this settles it instantly.
• The first band is often closer to the lead. Manufacturers put the first digit band nearer the end of the body; the tolerance band sits further in.

When none of the clues help, which happens with five-band brown-tolerance resistors that look symmetrical, read it both ways and ask which value is a standard one. 'Brown, red, black, black, brown' read backwards is 'brown, black, black, red, brown', which would be 100 × 100 = 10 kΩ, a real value, so in that case the ambiguity is genuine and the only reliable answer is a multimeter.

The mistakes that produce a value ten times out

• Reading from the wrong end, which usually turns the multiplier into a digit. A value with an odd leading digit and a strange multiplier is the symptom.
• Red versus orange, and brown versus red, under warm light or on a faded body. Move to daylight or a white LED, or tilt the resistor so the band catches the light; the colour differences are much clearer at an angle.
• Counting a reflection as a band, on glossy blue precision resistors in particular.
• Forgetting that black as a multiplier means ×1, so red-red-black is 22 Ω, not 220 Ω.
• Trusting the code on a resistor that has been hot. A scorched body shifts colours; measure it.

Checking the result with the resistor code and Ohm's law tools

Reading the code tells you what the resistor is supposed to be. Whether it is right for the job is a separate question, and that is where a calculator on the phone earns its place. Electrician Calculator Toolkit is a $3.99 one-time purchase for iPhone (iOS 17 or later, Data Not Collected on its privacy label, English plus 18 other languages) with eight NEC-based tools, two of which are for the bench rather than the panel.

• Resistor color code. Pick the bands and the tool decodes four- and five-band resistors with the tolerance, so a doubtful brown-or-red reading can be tried both ways in a second and compared with a standard value.
• Ohm's law. Enter any two of voltage, current, resistance and power and the other two appear. The question that actually matters at the bench is usually not 'is this 1 kΩ' but 'will 1 kΩ across 24 V dissipate more than the resistor's rating'. 24 V across 1,000 Ω is 24 mA and 0.576 W, which is too much for a quarter-watt part, and that is the kind of check the tool is for.

The app works entirely offline, which matters in a plant room with no signal, and it keeps every table it uses inside the app. The earlier posts in this series cover the other six tools: the wire size, voltage drop and conduit fill walkthrough and the box fill worked example. There is no Android version at the time of writing.

Quick reference

• Four bands: digit, digit, multiplier, tolerance.
• Five bands: digit, digit, digit, multiplier, tolerance.
• Black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9.
• Gold ×0.1 or ±5%, silver ×0.01 or ±10%, brown ±1%, red ±2%, no band ±20%.
• Gold or silver on one end means that end is the tolerance; read from the other end.
• When in doubt, measure.