Series and Parallel Resistor Calculator
Find the equivalent resistance of 2–20 ideal resistors in series or parallel. Enter a DC voltage to calculate current, voltage drop and power for every resistor.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
For series resistors, add the resistances and use the same current through each. For parallel resistors, add conductances (1/R) and use the same voltage across each branch. Apply V=IR and P=VI to each resistor.
series: R_eq=ΣR; parallel: 1/R_eq=Σ(1/R); total current=V/R_eq; power=VI
Worked example
100 Ω and 200 Ω in series give 300 Ω. At 12 V the current is 0.04 A, drops are 4 V and 8 V, and total power is 0.48 W. In parallel, the equivalent is about 66.6667 Ω and total current is 0.18 A.
Assumptions and input details
This handles a wholly series or wholly parallel ideal DC network, not mixed topologies or AC impedance. All resistance values must be strictly positive; ideal short circuits are outside this model. Supply voltage may be zero. All entered resistances share one selected unit. Real tolerance, heating, lead resistance and component power ratings are not inferred. The power chart compares dissipation in the entered ideal network.
References: OpenStax: resistors in series and parallel
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
SI prefixes are explicit: for example, milli means one thousandth, micro one millionth and kilo one thousand. Changing a unit changes the interpretation of the entered number.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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