Parallel Resistance Calculator
Enter any number of resistors wired across the same two points to get the equivalent parallel resistance and the current each one takes.
How it works
Resistors in parallel share the same voltage but split the current. Adding a second path makes it easier for current to flow, so the equivalent resistance always comes out lower than the smallest single resistor — the opposite of the series case.
The reciprocals add: 1/R_total = 1/R1 + 1/R2 + … Two equal resistors in parallel give exactly half the value, which is the shortcut most often used at the bench.
Current divides in inverse proportion to resistance, so the smallest resistor takes the largest share and dissipates the most power. That is the branch to check against its rating, not the largest one.
The formula
Equivalent resistance
1 ÷ R_total = 1/R1 + 1/R2 + 1/R3 + …
Two resistors (product over sum)
R_total = (R1 × R2) ÷ (R1 + R2)
n equal resistors
R_total = R ÷ n
Branch current
I_n = V ÷ R_n
Worked examples
| Scenario | Working | Result |
|---|---|---|
| Two 100 Ω in parallel | 100 ÷ 2 | 50 Ω |
| Three 1 kΩ in parallel | 1000 ÷ 3 | 333.33 Ω |
| 1 kΩ and 4.7 kΩ | (1000 × 4700) ÷ 5700 | 824.6 Ω — below the smaller one |
When you'd use it
- Getting a value below anything in your parts drawer
- Sharing current across resistors to spread the heat
- Working out the load several branches present together
- Checking what adding a pull-down does to an existing one
Common questions
Why is the total less than the smallest resistor?
Because each extra branch is another route for current. More routes means less total opposition, so the combination always conducts better than any single path in it. If your result is higher than the smallest value, something is wrong.
Can I use the product-over-sum shortcut for three resistors?
Only two at a time. Combine the first pair, then combine that result with the third. Applying it to three at once gives the wrong answer.
Which resistor gets hottest?
The smallest. They all see the same voltage, so the lowest resistance takes the most current and dissipates V² ÷ R — the most power. Size that one's rating first.
Does a 0 Ω resistor in parallel matter?
It shorts the combination — the equivalent resistance becomes zero and the other branches carry essentially nothing. This calculator ignores non-positive values rather than returning zero, since a 0 Ω entry is nearly always a typo.
Is anything I enter sent to a server?
No. Every calculation runs in your browser, so component values, circuit figures and measurements are never uploaded, logged or stored. There is no account and no record of what you typed.