Our Resistor Calculator helps you quickly compute equivalent resistance for series or parallel networks and, when a source voltage is provided, it reveals total current, voltage drops, and power dissipation across each resistor. Whether you are prototyping, studying for exams, or validating a design, this tool delivers accurate results in seconds.
What the Resistor Calculator Does
The calculator accepts up to ten resistor values in your preferred unit (ohms, kiloohms, or megaohms). Choose between series or parallel connection to get the equivalent resistance. If you add a source voltage, the tool will compute:
- Total current drawn by the network
- Voltage drop across each resistor (series) or branch voltage (parallel)
- Current through each resistor
- Power dissipated by each resistor and total power
How to Use the Resistor Calculator
- Select the connection type: Series or Parallel.
- Enter the number of resistors to include (2–10).
- Choose the resistor unit (?, k?, or M?).
- Fill in the first N resistor values. The calculator uses only the first N fields.
- Optionally enter a source voltage and pick its unit (V, mV, or kV) to compute current and power.
- Set your preferred decimal precision and click Calculate.
Series vs Parallel: The Basics
Series Networks
In a series connection, resistors are chained end to end. The same current flows through all components, and voltage divides proportionally to resistance. The equivalent resistance is the sum: Req = R1 + R2 + … + RN. If you provide a source voltage, the total current is simply V / Req. Voltage drop across each resistor is I × R, and power is I2 × R.
Parallel Networks
In a parallel connection, each resistor is connected across the same two nodes, so the voltage is the same on every branch. The equivalent resistance is found from conductances: 1 / Req = ?(1 / Ri). The total current is the sum of branch currents. Each branch current is V / Ri, and power in a branch is V2 / Ri. A 0 ? branch forms a short circuit that drives Req to 0 ? and indicates theoretically unbounded current—useful for diagnosing design errors.
Why This Calculator Helps
- Speed: Instantly check design alternatives without manual math.
- Clarity: Per-resistor results reveal where heat and voltage are concentrated.
- Accuracy: Unit-aware inputs prevent mistakes when mixing ?, k?, and M?.
- Design Safety: Power dissipation readouts help you choose the correct wattage rating.
Practical Tips for Better Circuit Results
When combining resistors to reach a target value, series connections increase resistance while parallel connections decrease it. If tolerances matter, consider using precision resistors or adding a trimming potentiometer. Always verify that each resistor’s power rating exceeds its calculated dissipation with margin (e.g., at least 2×). For battery-powered designs, note that higher equivalent resistance typically reduces current draw and extends runtime. When in doubt, simulate your circuit and compare the sim results to this Resistor Calculator for confirmation.
Example Use Case
Suppose you have three resistors: 220 ?, 330 ?, and 1 k?. In series, Req = 1,550 ?. With a 5 V source, the current is about 3.23 mA. You can then see voltage drops and power, ensuring each resistor’s wattage rating is sufficient. If you rewire the same parts in parallel, Req drops dramatically, increasing current, which may exceed your supply or thermal limits—an important insight this calculator reveals immediately.
Get Started
Enter your values above and click Calculate. With fast results and clear outputs, this Resistor Calculator is your reliable companion for labs, classrooms, and professional design benches.