Resistor Color Code Calculator

Through-hole resistors are too small to print a number on, so manufacturers paint a series of colored stripes around the body instead. A brown-black-red-gold resistor, for example, decodes to 1,000 Ω (1 kΩ) ±5% - the first two bands are the digits "1" and "0", the red band multiplies by 100, and the gold band sets a ±5% tolerance. This resistor color code calculator turns those stripes into a number for you: pick the color of each band and it returns the resistance in ohms, kilo-ohms, or mega-ohms, the tolerance, and the real-world range the resistor may measure.

How the resistance is calculated

The decoding rule is the same for every standard resistor; only the number of digit bands changes:

For a 4-band resistor you read two digit bands; for a 5-band resistor you read three. So brown-black-red (4-band) is the number 10 multiplied by 10² = 1,000 Ω, while brown-black-black-brown (5-band) is the number 100 multiplied by 10¹ = 1,000 Ω. The final tolerance band then sets how far the actual value may stray from that nominal figure.

The color-to-number key

Digit and multiplier bands share one sequence, which is worth memorizing because it underpins the whole system:

• Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4
• Green = 5, Blue = 6, Violet = 7, Grey = 8, White = 9
• Multiplier: the same numbers are used as a power of ten - red means ×10² = ×100. Gold means ×0.1 and silver means ×0.01 for small values.
• Tolerance: brown ±1%, red ±2%, green ±0.5%, blue ±0.25%, violet ±0.1%, grey ±0.05%, gold ±5%, silver ±10%.

How to use this calculator

You only need to look at the resistor and match colors. Work through the controls in order:

1. Pick 4-band or 5-band: count the stripes. Four total (including tolerance) is the most common general-purpose part; five total usually means a precision resistor.
2. Set the digit bands: choose the color of band 1, band 2, and (for 5-band) band 3 from the dropdowns. A color swatch shows next to each so you can match it to the part.
3. Set the multiplier: this is the band right after the digits and controls how many zeros (or which decimal place) the value lands on.
4. Set the tolerance: the band slightly set apart from the rest, often gold (±5%) or silver (±10%).
5. Press Calculate resistance: read the nominal value at the top, then check the min/max range and the band-by-band breakdown table below.

If you are not sure which end is which, start reading from the side where the bands are grouped tightest; the lone tolerance band sits on the opposite end.

A worked example: a 4.7 kΩ resistor

Suppose you have a 4-band resistor banded yellow-violet-red-gold. Yellow is 4 and violet is 7, giving the number "47". Red as a multiplier is ×10² = ×100, so 47 × 100 = 4,700 Ω = 4.7 kΩ. The gold tolerance band is ±5%, meaning the part may legitimately measure anywhere from 4,465 Ω to 4,935 Ω. That spread is why two resistors from the same bag can read slightly differently and both be correct.

Who this calculator is for

Anyone who has to turn colored stripes into a usable number benefits from it, including:

• Electronics hobbyists sorting a parts bin or following a breadboard tutorial.
• Students learning circuit basics who need to check homework answers against the color code.
• Makers and repair techs identifying a resistor before swapping it on a board.
• Hardware engineers sanity-checking a value quickly without pulling a datasheet.
• Teachers and kit builders who want a reliable reference to share with a class.

4-band vs 5-band resistors

The practical difference is precision. A 4-band resistor (two digits) covers everyday values where ±5% or ±10% is fine - pull-ups, current-limiting for LEDs, and general logic. A 5-band resistor (three digits) is used where you need a tighter tolerance such as ±1% or better, common in measurement, filters, and reference circuits. The extra digit lets the value be specified more exactly: 100 Ω can be written as brown-black-brown (4-band) or brown-black-black-black (5-band, ±1%).

Scenario comparison: same value, different parts

Here is how three common resistors decode, showing why the bands matter:

• Brown-black-orange-gold (4-band): 10 × 10³ = 10,000 Ω = 10 kΩ ±5% (range 9.5 kΩ - 10.5 kΩ).
• Red-red-brown-gold (4-band): 22 × 10¹ = 220 Ω ±5% (range 209 Ω - 231 Ω) - a classic LED resistor.
• Brown-black-black-red-brown (5-band): 100 × 10² = 10,000 Ω = 10 kΩ ±1% (range 9.9 kΩ - 10.1 kΩ) - the precision version of the first example, with a far tighter range.

What affects the real measured value

The color bands give the nominal value, but a multimeter may read something a little different. The main factors:

• Tolerance: the biggest factor - a ±10% part has twice the allowable spread of a ±5% part.
• Temperature: resistance shifts slightly with heat; precision parts list a temperature coefficient (ppm/°C).
• Lead and contact resistance: for very low values, the test leads and probe contact add a small amount.
• Aging and damage: overheated or stressed resistors can drift out of spec or read open.

Why resistors come in odd values (the E-series)

You will notice resistors are sold in values like 4.7 kΩ, 5.6 kΩ and 6.8 kΩ rather than tidy 5 kΩ or 6 kΩ steps. That is because resistors follow standard E-series ranges, where each value is spaced by a fixed ratio so that the tolerance bands of neighbouring values just touch and cover the whole number line with no gaps. The series you meet most often are:

• E6 (±20%): 6 values per decade - 1.0, 1.5, 2.2, 3.3, 4.7, 6.8.
• E12 (±10%): 12 values per decade, adding 1.2, 1.8, 2.7, 3.9, 5.6, 8.2 to the E6 set - this is where most hobby resistors live.
• E24 (±5%): 24 values per decade, the standard for general-purpose 4-band gold-tolerance parts.
• E96 (±1%): 96 values per decade, used by 5-band precision resistors, which is why they need a third digit band to express a value like 4.99 kΩ.

Knowing the series is a quick sanity check: if your decoded value is not close to a standard E-series number, you have probably misread a band or read the resistor from the wrong end.

Combining resistors in series and parallel

Decoding one resistor is often only the first step - in a real circuit you frequently need a value that no single part provides, so you combine several. The rules are simple once you have each resistance from the bands:

Two 1 kΩ resistors in series make 2 kΩ; the same two in parallel make 500 Ω. This is how makers hit a non-standard target - for example, putting a 10 kΩ and a 22 kΩ in parallel gives about 6.875 kΩ when the bag has no 6.8 kΩ part. Once you know each decoded resistance and how they combine, feed the total into the Ohm's Law Calculator to find the current or voltage at that point in the circuit.

Worked example: a current-limiting resistor for an LED

The most common reason hobbyists decode a resistor is to protect an LED. Suppose a red LED needs about 2 V across it and 20 mA (0.02 A) of current, driven from a 5 V supply. The resistor must drop the remaining 3 V, so by Ohm's law R = V ÷ I = 3 ÷ 0.02 = 150 Ω. Reaching into the parts bin, a brown-green-brown-gold resistor decodes to 1, 5, ×10¹ = 150 Ω ±5% - exactly right. If you only have a 220 Ω (red-red-brown-gold) part, the LED simply runs a little dimmer at about 13.6 mA, which is usually fine and safer. Decoding the band first, then checking it against the value the circuit needs, is the everyday workflow this calculator supports.

Special and hard-to-read resistors

A few parts do not follow the everyday pattern, and knowing them prevents head-scratching:

• Zero-ohm resistors carry a single black band and act as a wire jumper - handy for automated assembly. They have no meaningful resistance to decode.
• 3-band resistors omit the tolerance band entirely, which by convention means ±20%. Two digits and a multiplier are all you read.
• 6-band resistors add a temperature-coefficient band (ppm/°C) after the tolerance band - the first five bands still decode exactly like a 5-band part.
• Fusible and wirewound power resistors sometimes print the value as text instead of using colors, especially on larger bodies that have room for it.
• Faded or burned parts: heat can discolor bands until brown looks like red or orange. When in doubt, decode the best guess here and confirm the real value with a multimeter before trusting it.

Tips for reading bands accurately

• Find the tolerance band first: gold or silver almost always marks the right-hand (last) band, which fixes the reading direction.
• Use good light: brown, red, and orange can look alike under warm light; daylight or white LED helps.
• Confirm with a meter: if a band is faded or ambiguous, measure the resistor and match it to the nearest standard value.
• Watch for reversed parts: reading from the wrong end turns, say, a 330 Ω into a 33 Ω x large multiplier - the breakdown table here helps you catch it.

Color bands do not tell you the power rating

One thing the color code deliberately leaves out is the power rating - how many watts the resistor can dissipate before it overheats. Two resistors with the identical brown-black-red-gold bands (1 kΩ ±5%) can have very different power ratings: a tiny 1/8 W part and a chunky 2 W part look the same in code but are physically very different sizes. As a rough guide, body size signals wattage: through-hole resistors commonly come in 1/8 W, 1/4 W, 1/2 W, 1 W and 2 W, with each step noticeably larger. To check a resistor will survive in your circuit, work out the power it dissipates with P = I² × R or P = V² ÷ R, then pick a part rated for at least double that figure to leave headroom. Because none of this is encoded in the stripes, always confirm wattage from the datasheet or the printed value on the body for any power-handling application - the bands only ever give you resistance and tolerance.

Where the color code comes from

The colored-band system dates back to the 1920s, when the Radio Manufacturers Association standardized a way to mark components that were far too small to print numbers on. Assigning each digit a color - rather than a number - made values legible from any angle and survived the limitations of early printing. The scheme was later formalized internationally as IEC 60062, the same standard this calculator follows, which keeps the digit, multiplier and tolerance meanings consistent across manufacturers worldwide. That history is why the order of colors (black 0 through white 9) is fixed and worth memorizing: the same sequence has decoded resistors for roughly a century and appears on capacitors and other parts too.

Telling apart the colors that fool people

Most decoding errors trace back to a handful of look-alike colors, especially on small bodies or under warm lighting. A few habits help:

• Brown vs. red vs. orange: the classic mix-up. Brown is a dull, earthy tone, red is vivid, and orange leans toward amber. Compare them side by side under daylight or a white LED, not a yellowish bulb.
• Gold vs. yellow: gold has a metallic sheen and almost always sits at the far end as the tolerance band, while yellow is a flat digit color earlier in the sequence.
• Violet vs. blue vs. grey: on faded parts these blur together; tilt the resistor under light to catch the sheen difference, or measure to settle it.
• Black vs. a shadow: a genuine black band is matte and even; what looks like a faint extra band near a lead is sometimes just a shadow or printing smudge.

When two readings seem plausible, decode both here and keep the one that lands on a standard E-series value - the wrong reading usually produces an unusual number.

Key terms explained

• Significant digits: the first bands that form the base number before the multiplier is applied.
• Multiplier: the power of ten the digits are scaled by; it sets the magnitude (Ω, kΩ, MΩ).
• Tolerance: the ± percentage the real value may differ from nominal.
• Nominal value: the value the bands declare; the target the part is sorted to.
• Preferred (E-series) values: resistors come in standard steps (E12, E24, E96), which is why you see 4.7 kΩ but rarely 4.85 kΩ.

How this relates to your circuit math

Once you know the resistance, you usually need it for something - sizing a current-limiting resistor, checking a voltage divider, or estimating power dissipation. With the resistance in hand you can apply Ohm's law (V = I × R) and the power formula (P = I² × R) using the Ohm's Law Calculator. For long wire runs where the conductor's own resistance matters, the Voltage Drop Calculator is the right tool. This page handles the first step: getting an accurate resistance from the bands.

Limitations and assumptions

This is a decoding aid, not a measurement. Keep these limits in mind:

• It covers 4-band and 5-band through-hole resistors; it does not decode 6-band (temperature-coefficient) parts or 3-band (±20%) parts.
• It assumes the bands are read in the correct direction; a reversed part decodes to the wrong value.
• It does not read surface-mount (SMD) resistors, which use printed numeric codes rather than colors.
• The output is the printed nominal value and its tolerance window - it cannot tell you the true measured resistance of a specific part.
• It does not report power rating, which depends on the resistor's physical size, not its color bands.

How it compares to related tools

This page answers "what resistance do these bands mean?" If your question is different, a sister calculator fits better:

• To work out voltage, current, or power from the resistance, use the Ohm's Law Calculator.
• To size a wire run and check losses, use the Voltage Drop Calculator.
• For home projects, the BTU Calculator and Square Footage Calculator handle heating and area.

Sources

• International Electrotechnical Commission (IEC) - IEC 60062: Marking codes for resistors and capacitors.
• National Institute of Standards and Technology (NIST) - SI prefixes (kilo, mega) used for Ω, kΩ and MΩ.