Series Circuit Calculator
Calculate total resistance, current, and individual voltage drops for resistors connected in series.
Enter supply voltage and up to four resistance values.
In a series circuit, resistors are connected end-to-end so the same current flows through all of them. Voltage is shared among them; current is not.
Total resistance = R₁ + R₂ + R₃ + R₄
This is simply additive. Three 100 Ω resistors in series give 300 Ω total — no shortcuts.
Current = V / R_total (Ohm’s law)
The current is the same at every point in the circuit. This is the defining characteristic of series connections.
Voltage drop across each resistor = I × Rₙ
The voltage drops across each resistor are proportional to their resistance. A 100 Ω resistor in series with a 200 Ω resistor connected to 9 V: total R = 300 Ω, I = 0.03 A, V₁ = 3 V, V₂ = 6 V. The drops always add up to the supply voltage.
Practical uses: LED current-limiting resistors, voltage divider circuits, and understanding why a string of old Christmas lights goes dark when one bulb fails (all in series — one break and current stops for all).
Power dissipated in each resistor = I² × Rₙ = V_drop² / Rₙ. The resistor with the highest resistance dissipates the most power. In thermal design, this matters — the 200 Ω resistor in the example above burns 0.03² × 200 = 0.18 W, versus 0.09 W for the 100 Ω resistor.
Leave any resistor at 0 (or blank) to exclude it from the calculation.