Electric circuits come in many shapes and setups, but one of the most common — and useful — is the series-parallel circuit. It’s a combination of resistors connected both in series and in parallel, and calculating the current in these circuits can be easy when you follow the right steps.
Let’s break it down and make it simple.
Table of Contents
🔌 What Is a Series-Parallel Circuit?
A series-parallel circuit is a combination where:
- Some components are connected in series (one after another)
- Others are connected in parallel (side by side)
This setup is common in homes, cars, and electronics — giving the benefits of both circuit types.
⚡ Quick Recap: Series vs. Parallel
- In a series circuit, current is the same everywhere
- In a parallel circuit, voltage is the same across each branch, but current splits
So in a series-parallel circuit, you’ll need to:
- Find equivalent resistance
- Calculate total current
- Use Ohm’s Law (V = IR) to find current in individual branches
Use the calculator below to find the current in the series-parallel circuit.
Enter the voltage and series & parallel resistor values. The tool will calculate the total current and the current through each branch of the parallel resistor configuration.
🔣 Step-by-Step: How to Calculate Current
Step 1: Simplify the circuit
Break the circuit into series and parallel sections.
Step 2: Calculate total equivalent resistance
Use the formulas:
- Series:
R_total = R₁ + R₂ + R₃ ... - Parallel:
1 / R_total = 1 / R₁ + 1 / R₂ + 1 / R₃ ...
Step 3: Find total current using Ohm’s Law
Once you know the total resistance and the voltage source:
I_total = V / R_totalThis gives you the total current coming from the power source.
Step 4: Find current in each resistor
- For series resistors, current is the same
- For parallel resistors, use:
I_branch = V_branch / R_branchRemember: in parallel, the voltage across each branch is the same
💡 Example
Let’s say you have:
- A 12V battery
- Two resistors in parallel (R₁ = 6Ω, R₂ = 3Ω)
- One more resistor (R₃ = 2Ω) in series with the parallel group
- Parallel combination:
1/R_parallel = 1/6 + 1/3 = 0.5 → R_parallel = 2Ω - Total resistance:
R_total = 2Ω (parallel) + 2Ω (series) = 4Ω - Total current:
I_total = 12V / 4Ω = 3A - Voltage across the parallel branch:
V_parallel = 3A × 2Ω = 6V - Current through each parallel resistor:
I₁ = 6V / 6Ω = 1A I₂ = 6V / 3Ω = 2A
✔️ The current adds up: I₁ + I₂ = 1A + 2A = 3A
🛠️ Tools That Help
You can use:
- A multimeter to measure current and voltage
- A circuit simulator (like Falstad or Tinkercad)
- Or use the Free calculator on this page