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Decode 4-band resistor colour codes into resistance and tolerance, and combine two resistors in series or parallel. Full colour chart plus 5, 6-band and SMD codes below.
Series / Parallel
The 4-band code: Band1 + Band2 = first two digits; Band3 = multiplier; Band4 = tolerance. Read from the band closest to one end.
A resistor opposes the flow of current in a controlled, predictable amount. That sounds unglamorous, and it is the most common component in electronics precisely because so much circuit design comes down to limiting current or dividing voltage.
Its behaviour follows Ohm's Law exactly: the voltage across it equals the current through it multiplied by its resistance. For the underlying relationships, see our Ohm's Law calculator.
| Job | Example |
|---|---|
| Limiting current | Protecting an LED from the destructive current it would otherwise draw |
| Dividing voltage | Scaling a 12 V signal down to something a 3.3 V microcontroller pin can read safely |
| Pull-up and pull-down | Holding a digital input at a defined state instead of leaving it floating |
| Setting timing | With a capacitor, determining how fast a circuit charges or oscillates |
| Sensing current | A small known resistance producing a measurable voltage proportional to current |
Resistors are too small to print numbers on legibly, so the value is encoded in coloured bands. The scheme is defined internationally under IEC 60062 and has been essentially unchanged for decades.
| Colour | Digit | Multiplier | Tolerance | Temp. coeff. (ppm/K) |
|---|---|---|---|---|
| Black | 0 | ×1 | — | 250 |
| Brown | 1 | ×10 | ±1% | 100 |
| Red | 2 | ×100 | ±2% | 50 |
| Orange | 3 | ×1 k | — | 15 |
| Yellow | 4 | ×10 k | — | 25 |
| Green | 5 | ×100 k | ±0.5% | 20 |
| Blue | 6 | ×1 M | ±0.25% | 10 |
| Violet | 7 | ×10 M | ±0.1% | 5 |
| Grey | 8 | ×100 M | ±0.05% | 1 |
| White | 9 | — | — | — |
| Gold | — | ×0.1 | ±5% | — |
| Silver | — | ×0.01 | ±10% | — |
| Bands | Reading | Typical use |
|---|---|---|
| 4-band | digit, digit, multiplier, tolerance | General purpose, ±5% and ±10% carbon film |
| 5-band | digit, digit, digit, multiplier, tolerance | Precision metal film, ±1% and tighter |
| 6-band | as 5-band, plus temperature coefficient | Precision work where drift with temperature matters |
4-band example — yellow, violet, brown, gold: 4, 7, ×10, ±5% = 470 Ω ±5%, so anywhere from 446.5 to 493.5 Ω.
5-band example — brown, black, black, brown, brown: 1, 0, 0, ×10, ±1% = 1,000 Ω ±1%, so 990 to 1,010 Ω. Note how the third digit lets a precision part specify 1.00 kΩ rather than just 1 kΩ.
6-band adds a final band giving parts per million per kelvin — how much the resistance drifts as it warms. Brown is 100 ppm/K, red 50, blue 10. It only matters in precision analogue work; for hobby projects you can safely ignore it.
Work out the resistor you need for a circuit and the answer almost never matches a real part. That is not bad luck — resistors are manufactured only in preferred values, spaced logarithmically in standard series.
| Series | Values per decade | Matching tolerance |
|---|---|---|
| E6 | 6 | ±20% |
| E12 | 12 | ±10% |
| E24 | 24 | ±5% |
| E96 | 96 | ±1% |
| E192 | 192 | ±0.5% and tighter |
The E12 series is the one most hobby parts come from: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and the same figures in every decade — 100, 120, 150, and so on.
| E12 value | Next value | Step |
|---|---|---|
| 10 | 12 | 20.0% |
| 12 | 15 | 25.0% |
| 15 | 18 | 20.0% |
| 18 | 22 | 22.2% |
| 22 | 27 | 22.7% |
| 27 | 33 | 22.2% |
| 33 | 39 | 18.2% |
| 39 | 47 | 20.5% |
| 47 | 56 | 19.1% |
| 56 | 68 | 21.4% |
| 68 | 82 | 20.6% |
| 82 | 100 | 22.0% |
This is why your calculated 495 Ω becomes a 470 Ω part in practice, and why circuits are designed to tolerate that. If a design genuinely needs 495 Ω, you use a tighter series, combine two resistors, or reconsider the design.
A handful of E12 values cover the overwhelming majority of hobby circuits. If you are stocking a drawer, start here.
| Value | Colour bands (4-band, ±5%) | What it is usually doing |
|---|---|---|
| 100 Ω | Brown, black, brown, gold | Series protection on signal lines, LED on 3.3 V |
| 220 Ω | Red, red, brown, gold | LED current limiting on 5 V — the classic Arduino value |
| 330 Ω | Orange, orange, brown, gold | LED on 5 V at lower brightness, safe general choice |
| 470 Ω | Yellow, violet, brown, gold | LED current limiting on 12 V |
| 1 kΩ | Brown, black, red, gold | General purpose, transistor base resistor |
| 2.2 kΩ | Red, red, red, gold | Level shifting, I²C pull-ups on faster buses |
| 4.7 kΩ | Yellow, violet, red, gold | I²C pull-ups, general pull-up duty |
| 10 kΩ | Brown, black, orange, gold | The workhorse — pull-ups, pull-downs, voltage dividers |
| 100 kΩ | Brown, black, yellow, gold | High-impedance dividers, timing circuits |
| 1 MΩ | Brown, black, green, gold | Very high impedance, bleeder and gate pull-downs |
A 12 V supply, a red LED with a 2.1 V forward voltage, and a 20 mA target current.
| Step | Working | Result |
|---|---|---|
| Voltage the resistor must drop | 12 − 2.1 | 9.9 V |
| Ideal resistance | 9.9 ÷ 0.02 | 495 Ω |
| Nearest E12 value | — | 470 Ω |
| Actual current | 9.9 ÷ 470 | 21.06 mA |
| Power in the resistor | I²R = 0.02106² × 470 | 0.209 W |
Resistance is set by the colour bands. Power rating is set by physical size — a bigger body sheds heat faster. You cannot tell the resistance from the size, but you can usually tell the wattage.
| Rating | Typical body size | Where you see it |
|---|---|---|
| 1/8 W (0.125 W) | ~3.5 × 1.8 mm | Dense PCBs, signal circuits |
| 1/4 W (0.25 W) | ~6.3 × 2.3 mm | The default hobby part — most breadboard work |
| 1/2 W (0.5 W) | ~9 × 3.5 mm | LED circuits on 12 V, anything running warm |
| 1 W | ~11 × 5 mm | Power supplies, small loads |
| 2 W | ~15 × 5 mm | Higher-current circuits |
| 5 W and above | Ceramic block, ~22 × 9 mm | Wirewound, dummy loads, bleeder resistors |
| SMD package | Size (mm) | Typical rating |
|---|---|---|
| 0402 | 1.0 × 0.5 | 1/16 W |
| 0603 | 1.6 × 0.8 | 1/10 W |
| 0805 | 2.0 × 1.25 | 1/8 W |
| 1206 | 3.2 × 1.6 | 1/4 W |
Work out the dissipation with I²R or V²/R using the Ohm's Law calculator, then pick a rating at least double that figure.
| Combination | Series | Parallel |
|---|---|---|
| 100 Ω + 220 Ω | 320 Ω | 68.75 Ω |
| 470 Ω + 470 Ω | 940 Ω | 235 Ω |
| 1 kΩ + 10 kΩ | 11 kΩ | 909.09 Ω |
Two useful rules of thumb: parallel resistance is always lower than the smaller of the two, and two identical resistors in parallel give exactly half the value. That last one is the standard trick for hitting a value the E12 series does not offer.
SMD resistors are too small for bands and use printed number codes instead. If you are working on modern equipment or a commercial PCB, this is what you will actually encounter.
| Code style | How to read it | Example |
|---|---|---|
| 3-digit | Two digits then the number of zeros | 472 = 47 followed by 2 zeros = 4,700 Ω = 4.7 kΩ |
| 4-digit | Three digits then the number of zeros | 4701 = 470 followed by 1 zero = 4,700 Ω |
| R notation | R marks the decimal point | 4R7 = 4.7 Ω; R47 = 0.47 Ω |
| EIA-96 | Two digits index a lookup table, the letter is the multiplier | 01C = 100 × 100 = 10 kΩ |
| 000 or 0 | A zero-ohm link — a wire in resistor form | Used as a jumper on a PCB |
The 3-digit and 4-digit codes are straightforward once you see the pattern. EIA-96 is used on very small precision parts and needs a lookup table, because the two digits are an index rather than a value.
| Type | Typical tolerance | Best for | Watch out for |
|---|---|---|---|
| Carbon film | ±5% | General purpose, cheapest option | Noisier, drifts more with temperature |
| Metal film | ±1% or better | Precision, analogue and audio work | Slightly more expensive |
| Wirewound | ±1–5% | High power, current sensing | Inductive — unsuitable at high frequency |
| SMD thick film | ±1–5% | Modern commercial boards | Difficult to hand-solder at small sizes |
| Potentiometer | Variable | Volume controls, adjustable dividers | Wears out; wiper can go open circuit |
| Thermistor | Varies deliberately | Temperature sensing, inrush limiting | Resistance is meant to change — not a fault |
For most hobby work, ±5% carbon film is entirely adequate. Move to metal film when the circuit is analogue, when accuracy genuinely matters, or when noise is a concern.
The same handful of values do very different jobs depending on the circuit around them.
| Context | The resistor's job | Typical value |
|---|---|---|
| Arduino | Limiting LED current on a 5 V output pin; pull-down on a button input so the pin is not left floating | 220 Ω / 10 kΩ |
| Raspberry Pi | Protecting 3.3 V GPIO pins, which are not 5 V tolerant, and forming dividers to bring 5 V sensor outputs down safely | 1 kΩ / 10 kΩ pairs |
| I²C sensor buses | Pull-ups on the data and clock lines — the bus does not work without them | 4.7 kΩ |
| LED strips and panels | Series resistance per LED or per string, set by supply voltage and forward voltage | 220 Ω to 470 Ω |
| Audio amplifiers | Setting gain, forming input impedance and volume dividers — where metal film pays for itself in lower noise | 1 kΩ to 100 kΩ |
| Power supplies | Bleeder resistors discharging capacitors after power-off; feedback dividers setting output voltage | Varies; often high wattage |
| Solar and battery systems | Current shunts — a very low, precise resistance producing a measurable voltage proportional to current | 0.001 Ω to 0.1 Ω |
| Transistor circuits | Base resistors limiting drive current; emitter resistors setting bias | 1 kΩ to 10 kΩ |
How do I read resistor colour codes?
Start from the end where the bands are grouped closest together. On a 4-band resistor the first two bands are digits, the third is a multiplier and the fourth is tolerance. Yellow-violet-brown-gold is 4, 7, ×10, ±5% = 470 Ω. The tolerance band is usually gold or silver and sits slightly apart from the others.
How do I calculate a resistor value from the bands?
Combine the digit bands into a number, then multiply by the multiplier band. For 4-band: (first digit × 10 + second digit) × multiplier. For 5-band, combine three digits instead of two. Brown-black-black-brown-brown is 100 × 10 = 1,000 Ω ±1%.
What is resistor tolerance?
Tolerance is the guaranteed accuracy of the value. A 470 Ω ±5% resistor is guaranteed to measure between 446.5 Ω and 493.5 Ω. Gold is ±5%, silver ±10%, brown ±1% and red ±2%. Tighter tolerance costs more and is only worth paying for where accuracy genuinely affects the circuit.
What is the difference between 4-band and 5-band resistors?
A 5-band resistor has three digit bands instead of two, allowing a more precise value — 1.00 kΩ rather than 1 kΩ. They are usually precision metal film parts at ±1% or better. The important practical point is to count the bands before decoding, because reading a 5-band part as 4-band is out by roughly a factor of ten.
What does the sixth band mean?
The sixth band is the temperature coefficient in parts per million per kelvin — how much resistance drifts as the part warms. Brown is 100 ppm/K, red 50 and blue 10. It matters in precision analogue and measurement circuits, and can be safely ignored for general hobby work.
Why can't I buy the exact resistor value I calculated?
Resistors are made only in preferred values from standard series. E12 has twelve values per decade — 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 — and E24 has twenty-four. A calculated 495 Ω becomes a 470 Ω part. If you need something in between, combine two resistors or use a tighter series such as E96.
What resistor do I need for an LED?
Subtract the LED's forward voltage from the supply, then divide by the target current. For 12 V, a 2.1 V red LED and 20 mA: (12 − 2.1) ÷ 0.02 = 495 Ω, so use a 470 Ω part. Then check the wattage — I²R here is 0.209 W, which means a 0.5 W resistor rather than a 0.25 W one.
How do I read surface-mount resistor codes?
SMD parts use printed numbers, not colours. A 3-digit code gives two digits and a count of zeros, so 472 is 4,700 Ω. A 4-digit code gives three digits and a count of zeros. An R marks the decimal point, so 4R7 is 4.7 Ω. Very small precision parts use EIA-96, where two digits index a lookup table and a letter gives the multiplier.
How do resistors combine in series and parallel?
In series they simply add: two 470 Ω resistors give 940 Ω. In parallel, the combined value is (R1 × R2) ÷ (R1 + R2), so two 470 Ω resistors give 235 Ω. Parallel resistance is always lower than the smaller of the two, and two identical resistors in parallel give exactly half the value.
What is a zero-ohm resistor for?
It is a wire link in resistor form, marked 000 or 0. Automated assembly machines place resistors, not wires, so a zero-ohm part lets a manufacturer bridge two points on a board using the same equipment. They also allow one board design to be configured differently by fitting or omitting links.
What is the difference between carbon film and metal film resistors?
Carbon film is cheaper, typically ±5%, and slightly noisier with more drift over temperature. Metal film achieves ±1% or better with lower noise and better stability, at modest extra cost. Use carbon film for general purposes and metal film for analogue, audio and measurement circuits where accuracy matters.
Does a resistor's power rating matter?
Very much. The resistance sets the current; the power rating determines whether the part can dissipate the resulting heat. Calculate I²R and choose a resistor rated comfortably above it — running at more than about two-thirds of rating means a hot component that drifts in value and shortens its life.
Reading the bands is the easy part, and this page's decoder handles it. The steps that actually determine whether a circuit works are the ones after: choosing the nearest preferred value, and confirming the part can dissipate the power it will be asked to handle.
From here, the Ohm's Law calculator works out the resistance and power you need, the voltage drop calculator covers losses in cable runs, and the electricity cost calculator prices consumption.