Voltage Drop Calculator
Free online voltage drop calculator.
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What is Voltage Drop Calculator?
The Voltage Drop Calculator is a free electrical engineering tool that estimates how much voltage a wire run loses before it reaches the load. Enter the source voltage, load current, one-way length, system type, conductor material, and AWG size β and instantly see the drop in volts, the percentage drop against the common 3% and 5% limits, the voltage the load actually receives, and the power wasted as heat. It also recommends the smallest AWG conductor that passes each limit, with temperature-corrected resistivity for hot environments. Everything runs in your browser.
Key Benefits
- Size conductors correctly the first time instead of guessing and hoping
- Catch undersized wire before it browns out motors, LEDs, or electronics
- Compare copper vs aluminum instantly for the same run and load
- See wasted power in watts β the money burning in your conductors
- Get a minimum-AWG recommendation against 3% and 5% limits automatically
Common Use Cases
- β’Size 12 V or 24 V DC runs for solar, RV, marine, and IoT installations
- β’Check mains branch circuits meet code guidance before pulling cable
- β’Verify long three-phase runs to pumps, machines, and EV chargers
- β’Compare conductor cost: aluminum vs copper for the same drop budget
- β’Plan garden-lighting or outbuilding runs where distance kills voltage
Check Voltage Drop in a Cable Run
- Enter the circuit basics: Type the source voltage, the load current in amps, and the one-way run length, choosing metres or feet as the unit.
- Set conductor and system: Pick the material (copper, aluminum, silver, or gold), the AWG size from 4/0 down to 30, the conductor temperature, and whether the circuit is DC, single-phase AC, or three-phase AC.
- Read drop, loss, and limits: The result shows voltage drop in volts and percent, voltage at the load, one-way wire resistance, and power lost in the conductors, with pass or fail flags for the 3% and 5% limits.
- Resize if needed: If the drop fails, check the recommended minimum AWG cards for the 3% and 5% limits and pick that size β or Copy the full summary into your design notes.
Key Features
- DC, single-phase, and three-phase AC drop formulas in one tool
- Full AWG table from 4/0 (107 mmΒ²) down to 30 AWG with mmΒ² cross-sections
- Copper, aluminum, silver, and gold with temperature-corrected resistivity
- Colour-coded 3% / 5% pass-warn-fail banner with plain-language advice
- Minimum-AWG recommendation engine for both 3% and 5% limits
- 100% client-side β no signup, no server, works offline
Frequently Asked Questions
Which formula does the voltage drop calculation use?
It uses R = resistivity(T) x L / A with temperature-corrected resistivity, then Vd = 2 x R x I for DC and single-phase AC (both conductors carry current) and Vd = 1.732 x R x I for three-phase, matching standard electrical engineering practice.
Which materials, wire sizes, and systems are supported?
Copper, aluminum, silver, and gold conductors in AWG 4/0 down to 30, lengths in metres or feet, any conductor temperature (the reference is 20 degrees C), and DC, single-phase AC, or three-phase AC systems.
What do the 3% and 5% recommendations mean?
The result flags whether your drop is within the recommended 3% limit and the commonly accepted 5% ceiling, and the tool computes the minimum AWG (up to 4/0) that meets each limit for your current and run length.
How accurate are the results?
They model solid conductors from AWG cross-sections and temperature-adjusted resistivity, which is accurate for sizing estimates, but real installations must also follow ampacity tables and local electrical codes. All math runs in your browser.