4-Band Resistor Color Code Calculator: Read Any Resistor and Verify It

How to Read a 4-Band Resistor (The 4 Color Bands Explained)

Each of the four bands has a specific job, and the order never changes. Once you know the jobs, reading a resistor is no harder than reading a three-digit number.

Band 1 (first digit). This is the stripe closest to one end of the body. It gives you the tens digit of the two-digit base number. It can be any color from black (0) through white (9), but in practice it is never black because that would make the base number start with zero.

Band 2 (second digit). Immediately next to band 1. It gives you the ones digit of the base number. Any color from black (0) through white (9).

Band 3 (multiplier). This band tells you what to multiply the two-digit base number by. Black means multiply by 1, brown by 10, red by 100, orange by 1,000, and so on up through blue at 1,000,000. Gold and silver are special: gold means multiply by 0.1 and silver by 0.01, which is how you get values below 10 ohms.

Band 4 (tolerance). Sits at the opposite end of the body, usually with a visible gap between it and band 3. Gold means the actual resistance is within 5 percent of the labeled value. Silver means 10 percent. Brown is 1 percent, red is 2 percent. Most hobbyist parts are gold or silver.

The formula is straightforward: (digit 1 × 10 + digit 2) × multiplier = nominal resistance. The tolerance band then tells you the range of acceptable real-world values. A resistor labeled 4,700 ohms with a gold tolerance band can legally measure anywhere from 4,465 to 4,935 ohms.

If you want the full picture including 5-band and 6-band codes, power ratings, and E-series preferred values, the complete resistor guide covers all of it. This page stays focused on reading 4-band parts.

4-Band Resistor Color Code Chart and Quick Memory Tricks

The table below covers every color you will see on a 4-band resistor. The digit column applies to bands 1 and 2, the multiplier column applies to band 3, and the tolerance column applies to band 4. Not every color appears in every column. Gold and silver, for example, are only used as multipliers or tolerance indicators and never as digits.

The most popular mnemonic for the digit sequence is: "B.B. ROY of Great Britain has a Very Good Wife" where the first letter of each word maps to a color in order from 0 to 9. Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5), Blue (6), Violet (7), Grey (8), White (9). Say it once or twice and the digit values stick. For multipliers, notice that the pattern is just powers of ten following the same color order: black is 10^0 (which is 1), brown is 10^1 (which is 10), red is 10^2 (which is 100), and so on.

For tolerance, gold and silver are the two you will see most often. Gold is 5 percent and silver is 10 percent. If there is no fourth band at all, the tolerance is 20 percent, but that is rare on modern parts. The tighter tolerances (brown at 1 percent, red at 2 percent, green at 0.5 percent, blue at 0.25 percent, violet at 0.1 percent) appear on precision resistors that cost more and are less common in hobbyist kits.

Step-by-Step Example: Reading a Resistor from Left to Right

The best way to cement the color code is to work through real resistors. Below are three common values you will find in any starter kit. For each one, hold the resistor (or imagine holding it) with the gold or silver band on the right, then decode from left to right.

Example 1: Yellow, Violet, Red, Gold. Band 1 (yellow) = 4. Band 2 (violet) = 7. The two-digit base number is 47. Band 3 (red) = multiply by 100. So 47 times 100 = 4,700 ohms, or 4.7 kilohms. Band 4 (gold) = 5 percent tolerance. That means the real resistance can be anywhere from 4,465 to 4,935 ohms and the part is still within spec.

Example 2: Brown, Black, Orange, Gold. Band 1 (brown) = 1. Band 2 (black) = 0. Base number is 10. Band 3 (orange) = multiply by 1,000. So 10 times 1,000 = 10,000 ohms, or 10 kilohms. Band 4 (gold) = 5 percent tolerance, giving a range of 9,500 to 10,500 ohms.

Example 3: Red, Red, Brown, Silver. Band 1 (red) = 2. Band 2 (red) = 2. Base number is 22. Band 3 (brown) = multiply by 10. So 22 times 10 = 220 ohms. Band 4 (silver) = 10 percent tolerance, giving a range of 198 to 242 ohms. This is the classic LED current-limiting resistor. With a 9 V battery across it and nothing else in the loop, Ohm's law gives I = 9 / 220 = 0.0409 A, or about 40.9 mA. Many kits sell the same 220 ohm value with a gold band for 5 percent tolerance.

Notice how the same decoding process works every time. Two digits, one multiplier, one tolerance. The only variable is which colors you are looking at.

Test and Measure Your Resistor in CircuitForge 3D Simulator

Reading the bands gives you the labeled value, but you can go a step further and verify it against Ohm's law in a live simulation. CircuitForge lets you build a simple series circuit in the 3D view and compare the simulated current with what the math predicts.

Place a battery, a resistor and an Ammeter in a series loop. Wire them so current flows from the battery's positive terminal, through the resistor, through the Ammeter, and back to the battery's negative terminal. Set the resistor to the value you just decoded from the bands. Run the simulation and look at the Telemetry panel for the circuit-total current.

Now do the math yourself: I = V / R. If you used a 9 V battery and a 220 ohm resistor, the expected current is about 40.9 mA. The Telemetry reading should be close to that figure, though it may not match to the last decimal because real simulation involves rounding. The point is not exact agreement but confirmation that you read the bands correctly and that your mental math is in the right ballpark.

This loop of decode-predict-simulate is worth building into your workflow. It catches misreadings before they turn into debugging sessions on a real breadboard. If you need to measure current on a physical circuit, the technique is the same in principle: break the circuit, insert a meter in series, and compare the reading. See how to measure current for the full walkthrough with a real meter.

For everything beyond 4-band reading, including power ratings, E-series preferred values, and series/parallel math, the complete resistor guide picks up where this page leaves off.

Frequently Asked Questions

These are the questions that come up most often when people are learning to read 4-band resistors. Most of them boil down to two things: figuring out which end to start from and understanding what the tolerance band actually means in practice.

The gold-versus-silver question is by far the most common. Both are tolerance bands, and neither one is used as a digit, so spotting one tells you immediately which end of the resistor to read from. If you can identify that one band, the rest of the decoding falls into place.

The other frequent stumbling block is what happens when a resistor has no fourth band at all. Older resistors and very cheap ones sometimes leave the tolerance band off entirely, which means the tolerance is plus or minus 20 percent. That is a wide range, but the decoding process for the first three bands is identical.

If your question is about 5-band or 6-band resistors, power ratings, or series and parallel calculations, the complete resistor guide covers those topics in depth.