ELECTRONICS · CALCULATOR

Sum of resistors calculator

Free sum of resistors calculator: get series from resistance 1 and resistance 2. The formula and a worked example are shown; verify against the NEC.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Resistance 1

Resistance 2

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

Rseries = R1 + R2; Rparallel = R1R2 / (R1 + R2)

Two resistors, ideal values.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Resistance 1: 100 Ω · Resistance 2: 200 Ω

Series: 300 Ω · Parallel: 66.667 Ω

This example uses the stated inputs; results for the entered values appear above.

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