Parallel resistor calculator
Add resistor values in ohms (use k and M suffixes). Toggle between parallel and series. The reverse tool finds the resistor to add to hit a target.
What do I add in parallel to reach a value?
Formulas
Parallel: 1/Rt = 1/R1 + 1/R2 + … + 1/RnTwo in parallel: Rt = R1 × R2 ÷ (R1 + R2)Series: Rt = R1 + R2 + … + RnExample: 100 Ω ∥ 220 Ω = 22,000 ÷ 320 = 68.75 Ω. In series they make 320 Ω.
In parallel, current splits in inverse proportion to resistance: the smallest resistor carries the most current and dissipates the most power. Check each part's wattage with the Ohm's law calculator.
Questions people ask
What is the formula for resistors in parallel?
1/Rtotal = 1/R1 + 1/R2 + … For two resistors: Rtotal = R1 × R2 ÷ (R1 + R2). The total is always less than the smallest resistor.
What is the formula for resistors in series?
Rtotal = R1 + R2 + … Series resistance is always larger than the largest resistor.
What do two equal resistors in parallel give?
Half of one. Two 100 Ω resistors in parallel make 50 Ω, and each shares half the current.