Series: R_total = R1 + R2 + R3... Parallel: 1/R_total = 1/R1 + 1/R2 + 1/R3...
3 × 100Ω in series = 300Ω. Same 3 in parallel = 33.3Ω.
Use this calculator when you need a precise engineering result based on standard formulas. It is appropriate for design verification, academic coursework, and any scenario where the calculation needs to be defensible and repeatable.
Many engineering errors stem from applying a formula outside its valid range. Most standard engineering formulas have boundary conditions — material limits, temperature ranges, or loading assumptions — that must be satisfied for the result to be reliable.
An engineer compares two design options with different material grades. Running both through the relevant strength or stiffness calculation reveals which option meets the performance specification with an adequate safety factor, informing the material selection decision.
1/Rtotal = 1/R1 + 1/R2 + ... Or for two resistors: Rtotal = (R1 × R2)/(R1 + R2).
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