How to use this calculator
Pick series or parallel and enter the resistors (leave unused ones at 0). Add a supply voltage to get the current and power.
Formulas
SeriesReq = R1 + R2 + …
Parallel1Req = 1R1 + 1R2 + … (two resistors: R1R2R1 + R2)
Worked example
100, 220 and 330 Ω in parallel on 12 V (the default)
- 1/Req = 1/100 + 1/220 + 1/330 = 0.01758 S.
- Req = 56.9 Ω, smaller than the smallest resistor.
- I = 12/56.9 = 211 mA; P = 2.53 W.
Frequently asked questions
How do I handle a mixed network?
Reduce it in stages: combine resistors that are purely in series or purely in parallel, redraw, and repeat until one resistor is left.
Why is parallel resistance smaller?
Each resistor adds another path for current, so the total current goes up for the same voltage.