Configuration
Circuit diagram
Formulas
Series
Rtotal = R1 + R2 + โฆ + Rn
Same current through all resistors.
Voltage divides proportionally to resistance.
Total R is always larger than any single resistor.
Parallel
1/Rtotal = 1/R1 + 1/R2 + โฆ + 1/Rn
Same voltage across all resistors.
Current divides inversely to resistance.
Total R is always smaller than the smallest resistor.
Two resistors parallel
Rtotal = (R1 ร R2) / (R1 + R2)
Quick formula for 2 parallel resistors.
For equal values: Rtotal = R / n
Equal resistors
n identical resistors R in parallel:
Rtotal = R / n
n identical resistors R in series:
Rtotal = R ร n