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.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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