Total resistance
68.75 ohms
Free resistor network tool
Parallel Resistor Calculator
Calculate equivalent resistance for parallel branches and optionally solve branch current and branch power from a known supply voltage.
Electrical network calculator
Parallel resistor inputs
Total resistance plus branch current
Quick examples
Total current
0.174545 A
Supply voltage
12 V
Total power
2.094545 W
Branch breakdown
| Branch | Resistance | Current | Power |
|---|---|---|---|
| 1 | 100 ohms | 0.12 A | 1.44 W |
| 2 | 220 ohms | 0.054545 A | 0.654545 W |
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What is a parallel resistor calculator?
A parallel resistor calculator finds the equivalent resistance of two or more resistors connected in parallel. In a parallel network, each branch shares the same voltage, while the total current is split across the branches depending on each resistor value.
This makes the tool useful for electronics design, resistor-network planning, current sharing checks, educational circuit work, and troubleshooting situations where you need to know the combined resistance and, optionally, the branch currents at a known supply voltage.
Instead of only returning the equivalent resistance, this calculator can also show total current, branch current, and branch power when a voltage is provided, which makes it more useful in actual circuit planning.
Why parallel resistance behaves differently
Parallel networks do not add resistance the way series networks do. Every extra branch creates another path for current to flow, which reduces the overall resistance seen by the source. That is why the total parallel resistance is always lower than the smallest individual resistor in the network.
This matters whenever you combine resistors, split loads across branches, or compare what a source will actually see after several components are wired in parallel. It also matters for power, because each branch can dissipate a different wattage depending on its resistance.
More branches lower total resistance
Adding another parallel path gives current another route and reduces the overall equivalent resistance.
Each branch sees the same voltage
Branch voltage stays equal across the network, while current divides branch by branch.
Current splits by resistance
Lower-resistance branches draw more current than higher-resistance branches at the same voltage.
Power can differ per branch
Branch wattage changes with resistance, so one resistor may dissipate more heat than another.
How the parallel resistor formula works
The equivalent resistance of a parallel network is found by adding the reciprocals of the branch resistances, then taking the reciprocal of that total:
Core formula
1 / Rt = 1 / R1 + 1 / R2 + 1 / R3 + ...
Step 1: Add the reciprocal of each resistor
Each branch contributes 1 divided by its resistance value to the network total.
Step 2: Take the reciprocal of that sum
That gives the final equivalent resistance seen by the source.
Step 3: Apply the supply voltage if known
Once voltage is known, branch current, total current, and branch power can also be calculated.
Step 4: Compare the branch behavior
Branch current and power help show how the load is shared across the network.
Quick reference examples for parallel resistors
These examples show how the equivalent resistance drops as more parallel branches are added.
| Network | Equivalent resistance |
|---|---|
| 100 ohms || 100 ohms | 50 ohms |
| 100 ohms || 220 ohms | 68.75 ohms |
| 470 ohms || 680 ohms || 1000 ohms | 222.43 ohms |
| 1000 ohms || 1000 ohms || 1000 ohms | 333.33 ohms |
| 1000 ohms || 1000 ohms || 1000 ohms || 1000 ohms | 250 ohms |
How to use this parallel resistor calculator
- 1
Enter at least two resistor values
Add the branch resistances that are connected in parallel.
- 2
Add or remove branches as needed
The calculator works for simple two-resistor cases and larger parallel networks.
- 3
Add a supply voltage if you want current and power
Voltage is optional, but it makes the result much more practical for circuit work.
- 4
Review the total resistance and branch breakdown
Use the branch current and power results to see how the network really shares the load.
- 5
Compare against ratings
Check whether each resistor can safely handle its branch power dissipation.
Real-world uses, edge cases, and limitations
Useful for electronics and resistor networks
Helpful when combining standard resistor values to reach a lower equivalent resistance.
Useful for current-sharing checks
Branch current outputs show how much current each resistor path actually draws at the supply voltage.
Useful for branch power checks
Branch power helps verify whether each resistor wattage rating is high enough.
Limited to ideal resistor behavior
This calculator does not model tolerance, temperature effects, parasitics, or non-linear components.
Frequently asked questions
- What is the formula for resistors in parallel?
- Add the reciprocals of the resistors, then take the reciprocal of that sum.
- Is the total resistance higher or lower in parallel?
- It is always lower than the smallest individual resistor in the network.
- Why do branch currents differ in parallel?
- Each branch sees the same voltage, so lower-resistance branches draw more current.
- Do I need to enter voltage?
- No. Voltage is optional if you only need equivalent resistance, but it is needed for branch current and power.
Calculate equivalent resistance and branch behavior together
Use this parallel resistor calculator to solve total resistance quickly and, when voltage is known, see the actual branch currents and branch wattage that matter in real electronics work.