Parallel Resistor Calculator
Calculate total resistance for up to 5 parallel resistors with branch current distribution.
Component Values
Results
1/Rtotal = 1/R1 + 1/R2 + ...
Parallel Resistors Explained
In a parallel circuit, all resistors share the same voltage across their terminals. The total resistance is found from the reciprocal rule: 1/Rtotal = 1/R1 + 1/R2 + ... + 1/Rn. The result is always less than the smallest resistor in the network.
Current splits between parallel branches inversely proportional to resistance — a smaller resistor carries more current. This is exploited in current-sharing circuits, where multiple resistors (or transistors) share a high current to reduce per-component stress.
The two-resistor shortcut R1×R2/(R1+R2) is fast for hand calculations. For more resistors, either add them one pair at a time, or use the reciprocal sum directly. This calculator handles up to 5 resistors in parallel and also shows branch currents when a supply voltage is given.
Parallel Resistance
1/Rtotal = 1/R1 + 1/R2 + ... + 1/RnTwo resistors
Rtotal = R1 × R2 / (R1 + R2)Key Points
- Rtotal < min(R1, R2, ..., Rn) — always smaller than any single resistor
- Two resistors: Rtotal = R1×R2/(R1+R2)
- Each branch carries V/Rn — smaller R gets more current
- Equal resistors: Rtotal = R/n (n resistors in parallel)
Applications
- Achieving non-standard resistance values
- Current sharing in power circuits
- Low-impedance voltage dividers
- Parallel LED current distribution
Practical Examples
Two resistors in parallel: 1 kΩ and 100 Ω. The result is always less than the smaller value. Dominated by the smaller resistor.
R = (1000 × 100) / (1000 + 100) = 90.9 Ω (91% of 100 Ω)
Need a 250 Ω 4 W resistor. Use four 1 kΩ 1 W resistors in parallel to share load.
R = 1000 / 4 = 250 Ω · Total power rating = 4 × 1 W = 4 W
Formula Reference
Parallel resistance formulas
General: 1/Rt = 1/R1 + 1/R2 + 1/R3 + ...
Two resistors: Rt = (R1 × R2) / (R1 + R2)
Equal resistors: Rt = R/n (e.g., 3× 300Ω in parallel = 100Ω)Design Examples
Two 8Ω speakers wired in parallel to match a 4Ω amplifier output for maximum power transfer.
Rt = (8×8)/(8+8) = 4 Ω — matches 4Ω amplifier output
Need 1Ω 10W but only have 2Ω 5W resistors. Two in parallel doubles power handling.
2× (2Ω 5W) in parallel = 1Ω 10W
Paralleling 4× 1Ω resistors creates a low-value shunt. At 10A the voltage drop stays within ADC range.
4× 1Ω in parallel = 0.25 Ω · V_drop @ 10A = 2.5 V
Design tip
For n identical resistors in parallel, Rt = R/n.
Parallel combination is always less than the smallest resistor.
Use parallel resistors to achieve non-standard values or increase power rating.Did you know? When two equal resistors are placed in parallel, the result is exactly half the resistance. For unequal resistors, the equivalent is always less than the smallest. This principle is used in precision resistor networks to achieve values not available in standard E-series.