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Series and parallel resistance calculator

Combine 2–20 resistor values into one equivalent resistance, with clear series and parallel assumptions.

Combine resistors

Enter 2–20 ideal resistances in ohms, separated by commas. Each must be between 0.000000001 and 1000000000 Ω.

Example input: 1000, 2000. Decimal numbers and scientific notation (such as 1e3) are accepted; do not enter units in the list.

Worked example

Two resistors of 1000 Ω and 2000 Ω in series: R = 1000 + 2000 = 3000 Ω (3 kΩ). In parallel: 1/R = 1/1000 + 1/2000, so R ≈ 666.667 Ω. Two 10 kΩ resistors in parallel give 5 kΩ.

How the estimate works

Basis: for series, Req = R1 + R2 + …; for parallel, 1/Req = 1/R1 + 1/R2 + …. These formulas assume ideal resistors with the stated connections. No wiring, tolerance, power, temperature or safety checks are performed. The equivalent may be outside the per-resistor input range. These idealized calculations do not check every real-world limit. Work with safe low voltages and verify your design independently.

For the circuit assumptions, common mistakes and practical checks, read the worked guide.