Resistors in Series and Parallel Calculator
Resistors limit the current in a circuit. Wiring two of them in a line, or side by side, gives two different total resistances. This page shows both, so you can compare the wirings before you build anything.
Pick the wiring you want to see as the main answer.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
In series, the resistances add: the total is the first plus the second. In parallel, the total is the product divided by the sum, which is always smaller than the smaller of the two resistors.
These formulas assume ideal parts with exactly the stated values. Real resistors carry a tolerance, usually a few percent, so the actual total can differ a little.
Worked example
Two resistors of 100 ohms and 220 ohms come to 320 ohms in series and 68.8 ohms in parallel. For the wiring you chose, the total is 320 ohms.
Questions
Why is the parallel total smaller than either resistor?
Parallel branches give the current more than one path. Each path adds to the flow, so the total resistance falls.
Can I combine more than two resistors?
This page takes two at a time. For more, combine two, then combine that result with the next one.
Does tolerance change the total?
A little. Each resistor's marked tolerance means its real value may differ from the marking by that share.
More like this
- Wet Bulb CalculatorWet bulb temperature from air temperature and humidity.
- Impulse CalculatorImpulse from force and time, or mass and speed change.
- Earth Curvature CalculatorHow far the ground drops away over a distance.
- Viscosity CalculatorKinematic viscosity from dynamic viscosity and density.
- PCB Trace Width CalculatorTrace width for a current and a temperature rise.
- Lever Mechanical Advantage CalculatorEffort needed to move a load with a lever.