Enter Values
Formulas
Series: Rtotal = R1 + R2
Parallel: Rtotal = (R1 × R2) ÷ (R1 + R2)
If voltage is entered: I = V ÷ Rtotal and P = V × I.
Example
For 100 Ω and 220 Ω, the series resistance is 320 Ω. The parallel resistance is 68.75 Ω.
How Connections Behave
Series resistances add because the same current passes through each component. Parallel conductances add because each branch has the same voltage.
Two positive resistors in parallel always produce an equivalent resistance lower than the smaller resistor.
Practical Limits
Real resistors have tolerance, temperature coefficient, voltage limits, and power ratings. If voltage is entered, the displayed power is total circuit power, not the individual power in each resistor.
Check each resistor's individual voltage and power dissipation before selecting components.