Electrical calculators
Size the wire, the conduit and the breaker, and check voltage drop and service load against NEC tables.
Voltage Drop Calculator
Enter the wire size, length, load and voltage to get volts dropped, percent drop, voltage at the load and the wire size that keeps it under 3%.
Open the Voltage Drop CalculatorWire & conduit
Voltage Drop Calculator
Enter the wire size, length, load and voltage to get volts dropped, percent drop, voltage at the load and the wire size that keeps it under 3%.
Wire Size Calculator
Enter the load, voltage and run length to get the minimum wire gauge by ampacity and by voltage drop; the larger of the two is the wire to buy.
Conduit Fill Calculator
Add your wires or cables, pick the conduit and see the fill percentage, the smallest trade size that passes and a to-scale cross-section.
Box Fill Calculator
Box fill = conductors + clamps + fittings + 2 per device + grounds, each at its wire's volume; four 12 AWG wires, two grounds, a switch and clamps need 18 cubic inches.
Circuits & loads
Ohm's Law Calculator
Type any two values to get the other two, see which formulas were used on the wheel, and add up resistors in series or in parallel.
Amp Calculator
Pick what you know, watts, kVA, horsepower or amps, and the circuit type to get the current, the power and the breaker it needs.
Breaker Size Calculator
Enter the load and whether it runs for three hours or more to get the breaker size and the smallest wire that breaker may protect.
Electrical Load Calculator
Enter the floor area and your big appliances to get the calculated load in VA, the amps at 240 V and whether a 100, 150 or 200 A service covers it.
Lighting
Recessed Lighting Calculator
Recessed light spacing is half the ceiling height, so an 8 ft ceiling puts cans 4 ft apart and a 14 by 12 ft room takes 12 lights.
Lumens Calculator
Lumens needed = room area x footcandles for the room; a 15 by 12 ft living room at 15 lm/sq ft needs 2,700 lumens, or four 800 lumen bulbs.