Wire Size Calculator for AWG and mm² Conductors
This wire size calculator finds the correct electrical wire gauge for your circuit from the current, voltage, run length, and acceptable voltage drop. It is built for electricians, contractors, and DIYers who need a fast, defensible answer instead of guessing from a chart.
The tool checks two limits at once. Ampacity is the maximum current a wire can carry without overheating, based on NEC ratings, and voltage drop is the voltage lost over the length of the run. It then recommends the larger of the two sizes so your wiring is both safe and efficient, and it shows the result in both AWG and mm².
How to Use the Wire Size Calculator
Set the wire properties
Choose the Material (Copper or Aluminum), the Circuit Type (Single Phase or Three Phase), and the Installation Method (Conduit, Open Air, or Underground). These change the ampacity ratings and resistance used in the math.
Enter the circuit parameters
Type the Current in amps, the Voltage (for example 120V, 240V, or 480V), and the Wire Length as the one-way distance from the panel to the load. Set a Max Voltage Drop percentage — the default is 3%.
Switch units if you need to
Click the m / ft label next to Wire Length to toggle between meters and feet. Any value you have already entered is converted automatically.
Read the recommendation
Results update instantly. You get the recommended size in AWG and mm² with a badge showing whether it was set By Ampacity or By Voltage Drop, plus the actual voltage drop, power loss, and a size comparison table.
In a hurry? Open Quick Presets to auto-fill typical circuits such as a Household Outlet, Kitchen Circuit, Water Heater, Air Conditioner, EV Charger, Lighting Circuit, Solar Panel, or Main Panel Feed.
Features
Dual Sizing Criteria
Checks both ampacity and voltage drop, then recommends the larger wire so your run meets safety and performance at the same time.
Copper and Aluminum
Switch conductor material with one click. The calculator adjusts the ampacity ratings and resistance values for each metal automatically.
Single and Three Phase
Pick Single Phase for residential or Three Phase for commercial and industrial circuits, and the voltage-drop formula adapts.
Multiple Installation Methods
Choose conduit, open air, or underground so the ampacity used matches how your wire is actually run.
Real-Time Voltage Drop
The actual voltage drop in both volts and percentage refreshes as you type, with a warning when it crosses your limit or 5%.
Power Loss and Resistance
See the power dissipated as heat in the wire along with its total resistance and resistance per kilometer.
Size Comparison Table
Compare nearby wire gauges side by side with their ampacity, voltage-drop percentage, and an OK, Marginal, or Undersized status.
Meters or Feet
Toggle the length unit between meters and feet; existing values convert automatically so you never re-enter the run.
Quick Presets
One-tap setups for common circuits — outlets, EV chargers, A/C units, water heaters, solar, and main panel feeds.
AWG Reference Table
Expand the built-in table to browse standard sizes from AWG 14 up to 500 kcmil with mm², copper and aluminum ampacity, and resistance.
Frequently Asked Questions
How do I choose the right wire gauge?
Enter your circuit current, voltage, and one-way run length, then pick the material and installation method. The calculator sizes the wire for both ampacity and voltage drop and recommends the larger result, so the gauge it shows is safe to carry the current and keeps voltage loss within your limit.
What is the difference between ampacity and voltage drop?
Ampacity is the maximum current a wire can carry without overheating — it is a safety limit. Voltage drop is the voltage lost over the length of the run, which affects how well equipment performs. Both matter, so the calculator checks each one and recommends whichever demands the larger wire.
Why does the calculator recommend a larger wire than I expected?
Long runs cause more voltage drop, which can require a bigger wire than ampacity alone would. When the badge reads By Voltage Drop, length is the limiting factor. You can lower the required size by shortening the run or allowing a higher max voltage-drop percentage.
What maximum voltage drop should I use (NEC 3% / 5%)?
The NEC recommends a maximum of about 3% for a branch circuit and 5% for the total circuit (feeder plus branch combined). The default 3% suits most residential and commercial work. The tool flags a warning when the actual drop exceeds your limit or goes past 5%.
Should I use copper or aluminum wire?
Copper conducts better and needs smaller sizes but costs more. Aluminum is lighter and cheaper but needs larger sizes and special connectors. Copper is standard for most residential wiring, while aluminum is common for service-entrance cables and large feeders. Switch the Material toggle to compare the recommended size for each.
Is wire length one-way or round trip?
Enter the one-way distance from your panel to the load. The calculator accounts for the return path in its voltage-drop formula, multiplying by 2 for single-phase and by √3 for three-phase circuits.
Is this calculator suitable for all countries?
The ampacity ratings follow NEC tables common in North America, while the wire resistance values are universal. If your local code uses different ampacity tables, use the AWG reference table for the resistance data and check your local standards for the ampacity limits.
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