Circuits and conductors
Current divider
- where
- current through R₁ (A)
- total current (A)
- branch resistances (Ω)
Explain this equation
Works out how a total current splits between two parallel branches. Useful for parallel conductors and shunt paths. The calculator also shows the current in R₂.
I₁ is the current in the R₁ branch. Iₜ is the total current entering the pair. R₁ and R₂ are the two branch resistances.
Both branches have the same voltage across them, so the lower resistance takes more current. That is why I₁ uses the other branch, R₂, on top of the fraction.
Sense check: 3 A into 10 Ω and 20 Ω gives 2 A in the 10 Ω branch and 1 A in the 20 Ω branch. The two must add back to Iₜ, and I₁R₁ should equal I₂R₂.
Watch out: putting R₁ on top gives the other branch’s current, a common mix-up.
The smaller resistance takes the larger current. For two parallel branches, current in R₁ uses the other resistance R₂ in the numerator.
Check by calculating the common branch voltage: I₁R₁ should equal I₂R₂, and the two currents must add to total current.
Enter your values to see the result.
Common mistake
Putting R₁ in the numerator when finding its own branch current.
Limits
Two positive parallel resistances.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.