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Circuit Solver

Pick a circuit template, enter the source voltage and the resistor values, and get the full solution the way an examiner wants it written: equivalent resistance first, then total current, then the share taken by each element.

Circuit Solver — pick the shape, get the full working

Match your question to one of these circuit shapes, enter the given values, and the complete solution is worked out step by step — like a model exam answer.

Resistors in
Total resistance
Circuit current
R1 (100 Ω) drop
R2 (200 Ω) drop
R3 (300 Ω) drop
Total power
  1. 1.Given: V = 12 V, resistors: 100 Ω, 200 Ω, 300 Ω
  2. 2.FormulaR_total = R₁ + R₂ + … (series adds)SubstituteR_total = 100 + 200 + 300ResultR_total = 600 Ω
  3. 3.FormulaI = V ÷ R_total (same current everywhere)SubstituteI = 12 ÷ 600ResultI = 20 mA
  4. 4.FormulaV(R1) = I × R1SubstituteV(R1) = 0.02 × 100ResultV(R1) = 2 V (P = 40 mW)
  5. 5.FormulaV(R2) = I × R2SubstituteV(R2) = 0.02 × 200ResultV(R2) = 4 V (P = 80 mW)
  6. 6.FormulaV(R3) = I × R3SubstituteV(R3) = 0.02 × 300ResultV(R3) = 6 V (P = 120 mW)
  7. 7.Check (KVL): drops sum to 12 V = supply ✓
  8. 8.FormulaP_total = V × ISubstituteP = 12 × 0.02ResultP = 240 mW
Common trap: In series, the biggestresistor drops the most voltage — current is the same through all of them, so V = I × R scales with R. Many students expect the small resistor to "take more".

The formula

R_series = R₁ + R₂ + … ; 1/R_parallel = 1/R₁ + 1/R₂ + … ; I = V / R_total

V
source voltage (volts)
Rₙ
each resistor in the network (ohms)
R_total
equivalent resistance seen by the source (ohms)
I
total current drawn from the source (amperes)

Worked example

A 12 V supply feeds R₁ = 100 Ω in series with R₂ = 220 Ω parallel to R₃ = 330 Ω.

  1. Parallel pair first: R₂∥R₃ = (220 × 330) / (220 + 330) = 72600 / 550 = 132 Ω
  2. Total: R_total = 100 + 132 = 232 Ω
  3. Source current: I = 12 / 232 = 0.0517 A = 51.7 mA
  4. Across the parallel pair: V = 51.7 mA × 132 Ω = 6.83 V

R_total = 232 Ω, I = 51.7 mA, and 6.83 V appears across the parallel combination.

Where you'll use it

The bread-and-butter question in every basic electrical engineering paper, and the calculation you do before choosing a supply or checking whether a resistor is about to exceed its wattage.

The laws behind it

Parts this applies to

Resistor (fixed)Potentiometer / Rheostat / TrimmerResistor Array / NetworkThermistor (NTC / PTC)Varistor / MOVSupercapacitorLED (light-emitting diode)MOSFET

Related calculators

Ohm's Law CalculatorV = I × RSeries and Parallel Resistance CalculatorSeries: R = R₁ + R₂ + …Voltage Divider CalculatorV_out = V_in × R₂ / (R₁ + R₂)Thévenin and Norton Equivalent CalculatorV_th = open-circuit voltage