Resistor Calculator (Series & Parallel)

Combine resistors in series or in parallel to find the total resistance, and find the resistor needed to pair with a known one to reach a target total. Accepts common notation like 4.7k, 4k7, 1M5, 2R2, or plain ohms. Pairs with the Ohm's Law, LED Resistor, and Voltage Divider tools. Everything runs locally in your browser.

Resistor values (one per line, or comma/space separated)

Series: R_total = R₁ + R₂ + …. Parallel: 1/R_total = 1/R₁ + 1/R₂ + …. Notation: 1k=1000 Ω, 4k7=4.7 kΩ, 1M5=1.5 MΩ, 2R2=2.2 Ω, 470=470 Ω; the letters K, M, and R mark the multiplier (and may stand in for the decimal point). The "find" mode solves for the second resistor that reaches the target total: parallel R₂ = R₁·R_t / (R₁ − R_t), series R₂ = R_t − R₁. Everything runs locally — nothing leaves your browser.