Resistor Calculator
Calculate resistor values, color codes, and electrical resistance
Resistance
1000.00 Ω
Tolerance Range
950.00 Ω - 1.05 kΩ
Power & Current at Common Voltages
| Voltage | Current | Power |
|---|---|---|
| 5V | 5.0 mA | 0.03 W |
| 9V | 9.0 mA | 0.08 W |
| 12V | 12.0 mA | 0.14 W |
How it works
A resistor calculator decodes the colored bands on a resistor into its resistance value, and combines resistors in series or parallel. Each color maps to a digit; the bands give significant figures, a multiplier, and a tolerance.
Bands & combinations
Series: R = R₁ + R₂ + … Parallel: 1/R = 1/R₁ + 1/R₂ + …
- bands
- color-coded digits + multiplier + tolerance
- series/parallel
- how resistors are wired together
Worked example
- Two resistors: 100 Ω and 200 Ω
- Wired in series
- R = 100 + 200
300 Ω total (in parallel they'd be ~66.7 Ω).
Good to know
- Series resistances add; parallel resistances always total less than the smallest one.
- The color code: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9.
- The tolerance band (often gold ±5%) shows how much the real value can vary.
Related Calculators
Frequently Asked Questions
How do I read resistor color codes?
On a 4-band resistor, the first two bands are digits, the third is the multiplier, and the fourth is tolerance. For example, red-violet-yellow-gold is 27 x 10,000 = 270 kΩ at ±5%. Five-band resistors add a third digit for precision values.
How do resistors combine in series and parallel?
In series, resistances simply add: Rt = R1 + R2 + ... In parallel, 1/Rt = 1/R1 + 1/R2 + ..., and for exactly two resistors the shortcut is Rt = (R1 x R2) / (R1 + R2). Parallel total is always less than the smallest resistor.
What do the tolerance bands mean?
Tolerance is how far the actual value may stray from the marked value: gold is ±5%, silver ±10%, brown ±1%, and red ±2%. A 1 kΩ ±5% resistor can measure anywhere from 950 Ω to 1,050 Ω.
How do I choose a resistor power rating?
Calculate dissipation with P = I²R or P = V²/R, then pick a rating at least twice that value for safety margin. Common ratings are 1/8 W, 1/4 W, 1/2 W, and 1 W.
Why can't I buy a resistor with my exact calculated value?
Resistors come in standard E-series values (E12, E24, etc.), so you round to the nearest standard value — for example, a calculated 330.7 Ω becomes a standard 330 Ω. Combine resistors in series or parallel when precision matters.