Calculate total resistance for up to 10 resistors in series or parallel. Optionally enter a supply voltage to see current and power dissipation per resistor.
Calculate Total Resistance
V
For current & power calculation
Formulas
Resistors in Series
The total resistance is the sum of all individual resistances. The same current flows through every resistor.
Rtotal = R1 + R2 + R3 + … + Rn
Resistors in Parallel
The reciprocal of the total resistance equals the sum of reciprocals. The same voltage appears across every resistor.
The total is always larger than the biggest individual resistor. The same current flows through every resistor. Voltage is divided across them proportionally to their values.
How do you calculate resistors in parallel?▾
Use the reciprocal formula: 1/Rtotal = 1/R1 + 1/R2 + …
The total is always smaller than the smallest individual resistor. The same voltage appears across every resistor. Current splits between them inversely proportional to their values.
Shortcut for two resistors: Rtotal = (R1 × R2) / (R1 + R2)
What is the result of two equal resistors in parallel?▾
Two identical resistors R in parallel always give R/2. Example: two 470 Ω resistors in parallel = 235 Ω. This is a practical trick to get non-standard values from common parts.
When should I use series vs parallel?▾
Use series when: you need to increase total resistance, limit current, or create a voltage divider.
Use parallel when: you need to decrease resistance, share power across multiple resistors, or achieve a non-standard resistance value from standard parts.
Why put resistors in parallel to share power?▾
Each resistor dissipates power P = V²/R (parallel) or P = I²×R (series). If one resistor would exceed its power rating, you can split it into two parallel resistors of double the value — each dissipates half the power. This is common in high-current circuits where high-wattage resistors are hard to source.