Two parallel resistors have the same voltage across them. Enter the DC source voltage and both resistances to see how the current divides between the branches.

Formula: I₁ = V/R₁; I₂ = V/R₂; total I = I₁ + I₂; equivalent R = 1/(1/R₁ + 1/R₂); total W = V × total I

Worked example

At 12 V, a 100 Ω branch draws 0.12 A and a 200 Ω branch draws 0.06 A. Together they draw 0.18 A, have an equivalent resistance of about 66.667 Ω and dissipate 2.16 W.

Parallel means shared endpoints

Both resistors connect across the same two circuit nodes. The voltage is equal across the branches; their currents add at the source. These equations do not apply to two resistors connected end to end in series.

What the ideal DC model assumes

The source maintains the entered voltage. Wiring and source resistance are neglected, and the resistors are treated as constant, purely resistive loads. Real component tolerance and temperature can change the current. This is not a model for AC motors, transformers or reactive loads.

Total watts are shared between the resistors

The lower-resistance branch draws more current at the same voltage and therefore dissipates more power. For either branch, power is V²/R. Use the resistor-power calculator to inspect a branch; the calculated dissipation alone does not select a suitable component rating.

Explore the related calculation

For a different starting point, try the resistor power calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

openstax.org reference

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Parallel resistor current calculator

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