Resistor Calculator
Every resistor tells you its value with colored bands — if you can read them. Pick the bands on your resistor (4-band or 5-band), and this calculator decodes the value, tolerance and acceptable range instantly, with a color guide to help you identify bands on real components.
Resistor value
1 kΩ ± 5%
Range: 950 Ω to 1.05 kΩ
Color guide
Tolerance: brown ±1% · red ±2% · green ±0.5% · blue ±0.25% · violet ±0.1% · gold ±5% · silver ±10%. Read bands left→right with the tolerance band on the right.
How it works
- Choose 4-band or 5-band mode to match your resistor.
- Select the color of each band using the dropdowns (with color swatches).
- 4-band: digit, digit, multiplier, tolerance. 5-band: digit, digit, digit, multiplier, tolerance.
- The decoded value appears instantly — e.g. 10 kΩ ± 5% — with min/max range.
- Check the color guide below for how bands are ordered on a physical resistor.
The formula
4-band value
value = (d₁×10 + d₂) × 10^multiplier
Brown-black-red = 10 × 10² = 1,000 Ω (1 kΩ). The multiplier band is a power of ten (gold = ×0.1, silver = ×0.01).
Tolerance
range = value × (1 ± tolerance%)
A 1 kΩ ± 5% resistor measures between 950 Ω and 1,050 Ω. Tighter tolerances (1%, 0.5%) cost more but matter in precision circuits.
Worked example
Worked example
- A resistor with brown, black, red, gold bands
- Digits: brown=1, black=0 → 10; multiplier: red=10²; tolerance: gold=±5%
- Value = 10 × 100 = 1,000 Ω = 1 kΩ
1 kΩ ± 5% — range 950 Ω to 1,050 Ω. The most common resistor you'll meet in a lab kit.
Common mistakes
- Reading the bands from the wrong end — the tolerance band (gold/silver) marks the right side; it's usually separated slightly from the others.
- Confusing red (2) with orange (3) in bad light — check the color guide and the multiplier.
- Forgetting that gold/silver on a 4-band resistor are multipliers (×0.1 / ×0.01), not digits.
Frequently asked questions
How do I know which end to read from?
The tolerance band (gold, silver, or a thin brown) is usually on the right, slightly separated. Read left to right from the other end.
What does a 5-band resistor mean?
It has three digit bands instead of two — for higher-precision values (e.g. 10.0 kΩ ± 1%) common in modern electronics.
Why do resistors have a tolerance?
Manufacturing can't hit exact values cheaply. A ±5% resistor of nominal 1 kΩ is guaranteed between 950 Ω and 1,050 Ω.
Can I identify the wattage from color bands?
No — wattage is determined by physical size, not color bands. This calculator decodes value and tolerance only.
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