How is voltage distributed in a series circuit?

Voltage divides across each resistor proportionally to its resistance. Larger resistors get a larger share of the source voltage. The sum of all voltage drops equals the source voltage (Kirchhoff's Voltage Law).

What happens if one component fails open?

If any component in a series circuit fails open (disconnects), the entire circuit stops working because there is only one current path. This is a key disadvantage of series circuits.

How do I calculate power in a series circuit?

Total power = I² × RT = Vs × I = Vs²/RT. Each resistor dissipates Pn = I² × Rn. The sum of individual powers equals the total power.

Series Circuit Calculator

This calculator requires JavaScript. R_total = R₁ + R₂ + ... + R_n | I = V / R_total | V_n = I × R_n

R_T = R₁ + R₂ + R_n

I = V_s / R_T

V_n = I × R_n

P_n = I² × R_n

Series Circuit — Enter Source & Resistors

V Source Voltage

I Or Enter Current (optional)

Enter voltage and resistors

Series Circuit Results

RTotal
—
Ω

Current I

—

Total Power

—

Figure 1: In a series circuit, all components share the same current. The total resistance is the sum of all individual resistances, and the source voltage divides across each resistor proportionally.

Table of Contents

Fundamentals

What Is a Series Circuit?
Series Circuit Rules

Worked Examples

LED Current Limiting
Voltage Divider Chain
Finding a Missing Resistor

Deep Dive

Kirchhoff’s Voltage Law
Power Distribution
Series vs Parallel

Reference

Frequently Asked Questions
Related Circuit Analysis Calculators

What Is a Series Circuit?

A series circuit connects components end-to-end so there is only one path for current. The same current flows through every component, from the positive terminal of the source through each resistor and back to the negative terminal. If any component fails open, the entire circuit stops working because the single current path is broken.

Series circuits are fundamental to electronics — from simple LED current-limiting resistors to voltage divider chains and sensor circuits. The Voltage Drop Calculator provides a specialised tool for analysing voltage distribution in longer cable runs.

Series Circuit Rules

Current: The same current I flows through every component.
Resistance: R_T = R₁ + R₂ + … + R_n (resistances add).
Voltage: V_s = V₁ + V₂ + … + V_n (voltage drops add to source).
Power: P_T = P₁ + P₂ + … + P_n (powers add).

Worked Example — LED Current Limiting

Given: V_s = 12 V, R₁ = 1 kΩ, R₂ = 2.2 kΩ, R₃ = 4.7 kΩ

R_T = 1000 + 2200 + 4700 = 7900 Ω

I = 12 / 7900 = 1.519 mA

V₁ = 1.519m × 1000 = 1.519 V (12.7%)

V₂ = 1.519m × 2200 = 3.342 V (27.8%)

V₃ = 1.519m × 4700 = 7.139 V (59.5%)

The voltage drops add to exactly 12 V, confirming Kirchhoff’s Voltage Law. The largest resistor (4.7 kΩ) takes the biggest share of the voltage.

Worked Example — Voltage Divider Chain

Given: V_s = 9 V, R₁ = R₂ = 10 kΩ

R_T = 20 kΩ

I = 9 / 20000 = 0.45 mA

Each resistor drops 4.5 V — an equal split. The midpoint voltage is 4.5 V.

This is a simple voltage divider. The Current Divider Calculator handles the parallel equivalent where current splits rather than voltage.

Worked Example — Finding a Missing Resistor

Given: V_s = 24 V, I = 10 mA, R₁ = 1 kΩ. Find R₂.

R_T = V / I = 24 / 0.01 = 2400 Ω

R₂ = 2400 − 1000 = 1400 Ω

The Circuit Current Calculator can verify this result by computing the current for the complete circuit.

Kirchhoff’s Voltage Law

Kirchhoff’s Voltage Law (KVL) states that the sum of all voltages around any closed loop is zero. In a series circuit this means the source voltage equals the sum of all voltage drops: V_s = V₁ + V₂ + … + V_n. The KVL Circuit Calculator applies this law to more complex multi-loop circuits.

Power Distribution

Each resistor dissipates power P_n = I² × R_n. Since the current is the same through all resistors, the resistor with the highest value dissipates the most power. Total power equals V_s × I = I² × R_T. The Power Dissipation Calculator helps verify that each resistor’s power rating is adequate.

Series vs Parallel

In a series circuit, adding more resistors increases total resistance and reduces current. In a parallel circuit, adding more resistors decreases total resistance and increases total current. Most real circuits combine both series and parallel elements — the Thevenin and Norton equivalent calculators simplify these mixed networks.

Frequently Asked Questions

Does the order of resistors matter in a series circuit?

No. The total resistance and current are the same regardless of the order. The voltage drop across each resistor depends only on its value and the current, not its position in the chain.

What happens if one resistor is much larger than the others?

The large resistor dominates — it takes most of the voltage drop and most of the power. The smaller resistors contribute very little to the total. This is why precision voltage dividers use matched resistor values.

Can I use this calculator for components other than resistors?

Yes, for DC circuits you can enter any resistance value — including bulb filaments, heater elements, or wire resistance. For AC circuits with inductors and capacitors, use the Impedance Calculator in the AC Circuits section.

Why do Christmas lights go out when one bulb fails?

Traditional Christmas lights are wired in series. When one bulb burns out (open circuit), the single current path is broken and all bulbs go dark. Modern sets use shunt devices to bypass failed bulbs.

How do I verify my calculation?

Check that the sum of all voltage drops equals the source voltage (KVL). Also check that the sum of individual powers equals V × I. If these two checks pass, your calculation is correct.

Browse all Electronics Calculators →

Last updated: March 2026