Resistor Calculator
Decode 4/5/6-band color codes in both directions, solve Ohm's law, size LED series resistors, pick real E12/E24 parts, and read SMD markings — all in one free tool.
Resistor Color Code Decoder
Pick the band count, then tap each band's color — or flip to reverse mode and get the bands for any value.
Ohm's Law Calculator
Fill in any two values — the other two are solved instantly. V = I × R, P = V × I = V²/R = I²R.
LED Series Resistor Helper
R = (supply − LED forward voltage) ÷ LED current. Also get power dissipation and the buyable E12 part.
E12 / E24 Nearest Standard Value
Map any calculated resistance to a part you can actually buy.
SMD Resistor Code Reader
3-digit, 4-digit, R-decimal, and EIA-96 codes.
Quick reference
| Format | Rule | Example |
|---|---|---|
| 3-digit | XY × 10Z | 472 = 4.7 kΩ |
| 4-digit | XYZ × 10W | 1002 = 10 kΩ |
| R-decimal | R = decimal point | 4R7 = 4.7 Ω |
| EIA-96 | 2 digits → E96 table, letter → multiplier | 01C = 10 kΩ |
EIA-96 multiplier letters: Z=×0.001, Y/R=×0.01, X/S=×0.1, A=×1, B/H=×10, C=×100, D=×1000, E=×10000, F=×100000.
Resistor Color Code Chart (IEC 60062)
The complete reference table behind the decoder above. Digit bands use the first column; the multiplier band multiplies; tolerance and TCR apply to the last bands.
| Color | Digit | Multiplier | Tolerance | TCR (ppm/K) |
|---|---|---|---|---|
| Black | 0 | ×1 | — | 250 |
| Brown | 1 | ×10 | ±1% | 100 |
| Red | 2 | ×100 | ±2% | 50 |
| Orange | 3 | ×1k | — | 15 |
| Yellow | 4 | ×10k | — | 25 |
| Green | 5 | ×100k | ±0.5% | 20 |
| Blue | 6 | ×1M | ±0.25% | 10 |
| Violet | 7 | ×10M | ±0.1% | 5 |
| Gray | 8 | ×100M | ±0.05% | 1 |
| White | 9 | ×1G | — | — |
| Gold | — | ×0.1 | ±5% | — |
| Silver | — | ×0.01 | ±10% | — |
| Pink | — | ×0.001 | — | — |
| (no band) | — | — | ±20% | — |
Worked Examples
Methodology
- Color code (IEC 60062): 4-band = 2 digits + multiplier + tolerance; 5-band = 3 digits + multiplier + tolerance; 6-band adds TCR. Gold/silver/pink are multiplier-only (×0.1/×0.01/×0.001); gold/silver also serve as ±5%/±10% tolerance.
- Ohm's law: V = I×R; power P = V×I = V²/R = I²R. Any two of the four quantities determine the other two.
- LED sizing: the series resistor drops the excess voltage: R = (Vs − Vf) / If, dissipating P = (Vs − Vf) × If. The tool recommends the nearest E12 part plus the next value up (safer current).
- E-series: decade-normalized search over the E12/E24 preferred-value tables; values are exact table entries, never interpolated.
- SMD: 3-digit (XY×10Z), 4-digit (XYZ×10W), R-as-decimal-point, and EIA-96 (two-digit E96 index + multiplier letter, verified against manufacturer tables).
- Display: mantissas shown with 4 decimals and SI prefixes (k, M, G, m, µ). For critical circuits, always confirm with a multimeter.
Scope boundary
This tool covers resistor color-code decoding in both directions, Ohm's-law solving, LED series-resistor sizing, E12/E24 nearest-value picking, and SMD marking reading. Resistor networks in parallel — total resistance, current division, power per branch — live in the dedicated parallel-resistor tool. Planned companions (not yet published): resistor-noise (Johnson thermal noise) and resistor-voltage-drop.
Frequently Asked Questions
How do I read a 4-band resistor color code?
Read the first two bands as digits, the third as the multiplier, and the fourth as tolerance. Example: brown-black-red-gold means digits 1 and 0, multiplier ×100, tolerance ±5%, so 10 × 100 = 1000 Ω ±5% (1 kΩ ±5%). Hold the resistor with the tolerance band (gold or silver) on the right.
What is the difference between 4-band, 5-band, and 6-band resistors?
4-band resistors have 2 significant digits, a multiplier, and tolerance — fine for ±5% and ±10% parts. 5-band resistors add a third significant digit for tighter values such as 10.0 kΩ ±1%. 6-band resistors add a sixth band for the temperature coefficient (TCR) in ppm/K, which tells you how much the resistance drifts with temperature. Use this tool's band selector to decode any of the three.
What do the gold and silver bands mean on a resistor?
As the last band, gold means ±5% tolerance and silver means ±10%. As the multiplier (third band on a 4-band resistor), gold means ×0.1 and silver means ×0.01 — that is how you get values like 4.7 Ω (yellow-violet-gold-gold) or 0.47 Ω (yellow-violet-silver-silver).
How do I find the color bands for a resistor value I need?
Use the reverse mode: enter the resistance, pick 4, 5, or 6 bands and a tolerance, and the tool shows the exact band colors. For example, 1 kΩ ±5% in 4-band is brown-black-red-gold, and 10 kΩ ±1% in 5-band is brown-black-black-red-brown.
What is resistor tolerance and why does it matter?
Tolerance is the maximum the real resistance may differ from the printed value. A 1 kΩ ±5% resistor can actually be anywhere from 950 Ω to 1050 Ω. Use ±1% or tighter for precision circuits like dividers and sensor front-ends; ±5% is fine for LED current limiting and pull-ups.
What is TCR on a 6-band resistor?
TCR (temperature coefficient of resistance) is the sixth band, given in ppm/K. A 100 ppm/K resistor changes at most 0.01% per degree Celsius. Brown = 100, red = 50, orange = 15, yellow = 25, blue = 10, violet = 5 ppm/K. It matters in precision analog circuits exposed to temperature swings.
How do I use Ohm's law to find voltage, current, or resistance?
V = I × R. Give the calculator any two of voltage (V), current (I), resistance (R), or power (P) and it solves the other two — for example 12 V across 100 Ω gives I = 12/100 = 0.12 A and P = 12 × 0.12 = 1.44 W.
How do I calculate how much power a resistor dissipates?
Use P = V × I, P = V²/R, or P = I²R — whichever matches what you know. Then pick a resistor wattage rating at least double the dissipated power: a resistor burning 0.2 W should be rated 0.5 W or higher so it runs cool and reliable.
What resistor do I need for an LED?
R = (supply voltage − LED forward voltage) / LED current. For a 12 V supply, 2 V LED, 20 mA: (12 − 2) / 0.02 = 500 Ω. The nearest standard E12 value is 470 Ω, which gives about 21 mA — close enough for most indicator LEDs. The helper also shows power dissipation and the next-safe E12 value up.
What are E12 and E24 resistor values?
E12 and E24 are standard series of preferred values so manufacturers only stock sensible steps: E12 has 12 values per decade (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82) and E24 has 24. The nearest-value finder maps any calculated resistance to the closest real part you can actually buy.
How do I read SMD resistor codes?
3-digit: first two digits are the value, third is the multiplier — 472 = 47 × 100 = 4.7 kΩ. 4-digit: same with three significant digits — 1002 = 100 × 100 = 10 kΩ. An R marks the decimal point: 4R7 = 4.7 Ω. EIA-96 (1% parts): two digits index the E96 table and a letter sets the multiplier — 01C = 100 × 100 = 10 kΩ.
Which nrtechstudio tool should I use for resistor networks?
This tool decodes color codes, solves Ohm's law, sizes LED resistors, and picks E12/E24 values. For two or more resistors wired in parallel — total resistance, current sharing, and power per branch — use the dedicated parallel-resistor tool. Planned companions cover resistor noise and voltage drop.
Is my data sent anywhere when I use this calculator?
No. This tool runs 100% in your browser — every calculation happens locally in JavaScript and nothing you type is uploaded, stored, or tracked. You can even disconnect from the internet after the page loads and it keeps working.
Why is my resistor getting hot, and what wattage do I need?
Heat means it is dissipating real power: compute P = V²/R or P = I²R. If the rating is close to P, the part runs hot and drifts. Rule of thumb: rate the resistor at least 2× the dissipated power — e.g. 0.25 W dissipated → use a 0.5 W part — and keep hot resistors away from temperature-sensitive components.
Free tool by NRTechStudio