Calculate the proper wire size, gauge, and electrical requirements for your electrical projects. Determine voltage drop, ampacity, and wire specifications with precision and safety standards compliance.
Gauge
-
Area (A)
-
Diameter (d)
-
Input the total amperage that will flow through the wire based on your electrical load requirements.
Enter the total wire length from the power source to the load, including any return path.
Choose voltage level, acceptable voltage drop percentage, and wire material type.
Receive recommended wire gauge, actual voltage drop, and safety compliance information.
The results block shows the recommended AWG, conductor area in square millimeters, and diameter. It assumes THHN/THWN conductors at 75C, matching most breaker terminations per NEC 110.14(C). If you choose three-phase, the note reminds you to pull three current-carrying conductors plus an equipment grounding conductor.
Load 50A, voltage 240V single-phase, one-way distance 180 ft, copper, 3% drop target, ambient 75F. The calculator returns #4 AWG copper (~21.2 mm2, diameter ~5.2 mm) with about 2.9% voltage drop (~6.96V). Switching to aluminum suggests #2 AWG to hold 3%. Both satisfy ampacity and keep motor starting torque healthy.
If the run lengthens to 250 ft, upsizing to #3 copper or 1/0 aluminum restores a sub-3% drop. Use the distance field to test what-if scenarios before you buy cable.
For sensitive electronics or data rooms, aim for 2% total drop. That may mean moving to a thicker gauge or stepping voltage up to 240V when equipment allows.
The calculator uses the K-factor method from NEC Chapter 9, Table 8.
Single-phase: VD = (2 x K x I x L) / CM. Three-phase:
VD = (1.732 x K x I x L) / CM. K is 12.9 for copper and
21.2 for aluminum at 75C; I is load current; L is one-way length in
feet; CM is circular mil area.
Ampacity is checked against the 75C column of NEC Table 310.16. If voltage-drop sizing produces a conductor smaller than required ampacity, the tool bumps up to the next AWG so you meet both thermal and performance limits.
Temperature input adjusts resistivity via each material's temperature coefficient. That covers rooftop conduits in Texas heat, bundled feeders in trays, or attic runs where ambient easily exceeds 90F, all of which raise voltage drop.
This quick reference closes the biggest gap we saw in competitor pages: a simple, field-ready distance chart that pairs voltage-drop targets with material choices. Values assume 75C conductors, single-phase 120V unless noted. Always confirm with your exact load in the calculator.
For feeders above 60A, aluminum can cut material cost by 30-50%. Use these starting points and verify with the calculator:
In humid states like Florida, favor copper or corrosion-inhibited aluminum terminations; coastal salt spray accelerates oxidation. In California (Title 24 inspections), inspectors often ask for voltage-drop calcs on EV and HVAC circuits�keep a PDF of this calculator's results with the permit set.
These distances come straight from the K-factor math using circular mil area and align with the ampacity chart, giving you a fast reality check before pulling conductors. Combine with conduit fill and temperature correction when multiple circuits share a raceway.
Explore our comprehensive collection of construction and electrical calculators
Calculate area measurements for flooring, painting, and construction projects with multiple room support.
Determine the amount of gravel needed for driveways, pathways, and landscaping projects.
Calculate tile quantities needed for floors, walls, and backsplashes with waste factor included.
Calculate heating and cooling requirements for HVAC systems based on room size and conditions.
Estimate asphalt quantities for paving projects including driveways, parking lots, and roads.
Calculate concrete volume and materials needed for foundations, slabs, and construction projects.
Enter 100A, your voltage, and distance. At 240V and 75 ft, #3 copper or 1/0 aluminum keeps voltage drop near 3% while satisfying ampacity. Longer runs may need 2 AWG copper.
At 30A over 200 ft, 8 AWG copper lands around 3% drop; 6 AWG aluminum is a common alternative. Enter your exact numbers to confirm before buying cable.
Ampacity is thermal; voltage drop is performance. A conductor might pass ampacity but still be too small for a long run. The calculator checks both so you do not meet code on paper yet fail in real use.
Copper has lower resistance and smaller diameter; aluminum is lighter and cheaper but needs larger size and AL/CU-rated lugs. For feeders over 60A and 100+ ft, properly sized aluminum often wins on cost.
Roughly 45 ft one-way at 120V keeps drop near 3%. At 240V, the same 12 AWG can go about 91 ft. Beyond that, upsize to 10 AWG to stay within NEC guidance.
NEC informational notes recommend 3% on branch circuits and 5% total. California Title 24 reviewers often want proof for EV and HVAC circuits; Florida coastal AHJs may also ask for corrosion-rated terminations alongside voltage-drop calcs.
Use the charger�s continuous load (typically 80% of breaker). For a 48A charger on a 60A breaker at 60 ft, 6 AWG copper keeps drop around 2%. Enter your run to confirm and check panel capacity.
Most 50A welder receptacles use 6 AWG copper up to ~100 ft. Longer shop runs can move to 4 AWG copper or 2 AWG aluminum to keep drop under 3% and maintain arc stability.
Yes. Attic runs in Arizona or rooftop conduits can exceed 90F ambient, reducing ampacity. Increase the temperature input to see how higher resistance pushes you to a larger gauge.