Resistor Calculator
Calculate resistor values
Frequently Asked Questions
How do I read resistor color codes?
Each color band represents a digit or multiplier. For a 4-band resistor: Band 1 (1st digit), Band 2 (2nd digit), Band 3 (multiplier), Band 4 (tolerance). Brown-Black-Red-Gold = 10 × 100 = 1kΩ ±5%.
What do the resistor color bands mean?
Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9. Multiplier bands: Gold=0.1, Silver=0.01. Tolerance: Gold=±5%, Silver=±10%, Brown=±1%.
How do I calculate total resistance in series and parallel?
Series: R_total = R₁ + R₂ + R₃. Parallel: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃. Three 100Ω resistors in series = 300Ω. In parallel = 33.3Ω. The calculator handles both configurations with any number of resistors.
What is the E-series for standard resistor values?
The E12 series has 12 values per decade: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82. E24 has 24 values for tighter spacing. The calculator suggests the nearest standard value for any calculated resistance.
How do I choose the right resistor wattage?
Power dissipated: P = I² × R or P = V²/R. Choose a resistor rated at least 2× the calculated power for safety. A 1kΩ resistor with 10V across it dissipates 0.1W — use a 0.25W resistor minimum.