4 Band Resistor Calculator: Read Color Codes

A 4 band resistor calculator decodes the resistance and tolerance represented by a resistor’s colored bands. Enter the first three band digits and the fourth-band tolerance to get the resistance value and its allowed range, useful for electronics students, hobbyists, and anyone checking a component before fitting it.

Formula

For a four-band resistor, the first and second bands form a two-digit number, and the third band multiplies it. The fourth band gives the tolerance: R = (10d₁ + d₂) × M, where R is nominal resistance in ohms (Ω), d₁ and d₂ are the first and second band digits, and M is the multiplier in ohms. The tolerance range is Rmin = R(1 − T/100) and Rmax = R(1 + T/100), where T is the fourth-band tolerance in percent.

Digit colors run from black 0 through brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, and white 9. Multiplier bands use powers of ten: black ×1, brown ×10, red ×100, and so on; gold means ×0.1 and silver ×0.01. Common tolerance bands include brown ±1%, red ±2%, gold ±5%, and silver ±10%; an unmarked fourth band commonly indicates ±20%.

Worked Example

The calculator defaults are brown, black, black, and brown. Brown is digit 1, black is digit 0, the black multiplier is ×1, and the brown tolerance is 1%.

Nominal resistance: (10 × 1 + 0) × 1 = 10 Ω.

Minimum: 10 × (1 − 1/100) = 9.90 Ω.

Maximum: 10 × (1 + 1/100) = 10.10 Ω.

The result is a nominal 10 Ω resistor with a tolerance range of 9.90–10.10 Ω.

1. Decode the First Two Significant Digits

The first band is the tens digit and the second is the ones digit: brown followed by black makes 10, while red followed by violet makes 27. The sequence matters, so reversing those bands changes the value; 27 and 72 are not interchangeable readings.

2. Apply the Multiplier Band

The third band scales the two-digit value, rather than adding another significant digit. For example, yellow-violet-red is 47 × 100, or 4,700 Ω (4.7 kΩ), while yellow-violet-gold is 47 × 0.1, or 4.7 Ω.

3. Interpret Tolerance as a Range

The fourth band tells how far the actual resistance may vary from its nominal value under the conditions specified for the component. A 1 kΩ resistor with a gold band has ±5% tolerance, so its nominal range is 950–1,050 Ω; tolerance is not an additional multiplier on the color-code digits.

4. Check Band Direction Before Reading

Four-band resistors generally have the tolerance band spaced slightly apart from the other three, which helps identify the reading direction. If the colors do not make sense when read one way, inspect the spacing and component markings rather than assuming the isolated-looking band is the first digit.

How to Choose

Choose a calculator that explicitly supports four-band codes and includes both gold and silver multipliers; these are easy to overlook but represent fractional multipliers, not large values. Check that it treats the fourth band as tolerance and reports a nominal value separately from the tolerance limits. The tool here is suitable when the bands are clear and the resistor follows the standard color code; if a component has five or six bands, use a calculator designed for that format instead.

Color perception can be affected by lighting, faded paint, and similar-looking colors such as red and brown. Use bright, neutral light, rotate the part to locate the tolerance band, and compare the result with the circuit diagram or a resistance measurement when the exact value is important. A multimeter can check a component, but in-circuit readings may be affected by other electrical paths; isolate one lead when a reliable standalone measurement is needed, and ensure the circuit is powered off before measuring resistance.

Results are stated in ohms. Divide by 1,000 to express ohms as kilohms (kΩ), or by 1,000,000 for megohms (MΩ); for instance, 4,700 Ω = 4.7 kΩ. The displayed limits are arithmetic bounds from the stated tolerance and do not account for temperature changes, aging, measurement uncertainty, or a resistor’s power rating.

Frequently Asked Questions

How do I read a four-band resistor?
Read the two significant-digit bands first, then the multiplier, and finish with the tolerance band. The tolerance band is often spaced farther from the other three.

What does a gold multiplier band mean?
Gold means multiply the two-digit value by 0.1. For example, red-violet-gold gives 27 × 0.1 = 2.7 Ω.

What does a gold tolerance band mean?
When gold is the fourth band, it indicates ±5% tolerance. Its meaning depends on its position: as the third band it is a multiplier, and as the fourth it is tolerance.

Can I use this for a five-band resistor?
No. Five-band codes use three significant digits before the multiplier, so use a five-band calculator to avoid decoding the wrong value.

Why does my meter show a different resistance?
A resistor’s actual value can differ within its tolerance, and measurement accuracy and circuit connections can also affect the reading. Measure with power off and, for an isolated value, disconnect one lead from the circuit.

Final Thoughts

Identify the resistor’s reading direction, enter the first two digits, multiplier, and tolerance, then check both the nominal value and its range. For unusual band counts or unclear colors, confirm the code with a suitable meter or component documentation before using the part.

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sel d1 | First band digit | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9
sel d2 | Second band digit | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9
sel mult | Multiplier | Silver=0.01, Gold=0.1, Black=1, Brown=10, Red=100, Orange=1000, Yellow=10000, Green=100000, Blue=1000000, Violet=10000000, Gray=100000000, White=1000000000
sel tol | Tolerance percent | Brown=1, Red=2, Green=0.5, Blue=0.25, Violet=0.1, Gray=0.05, Gold=5, Silver=10, None=20
out resistance | Resistance | ohm | (d1 * 10 + d2) * mult | 2
out minimum | Minimum resistance | ohm | resistance * (1 - tol / 100) | 2
out maximum | Maximum resistance | ohm | resistance * (1 + tol / 100) | 2