Copper
Electrical calculators
Which conductor carries the load, how many fit in the raceway, how many volts you give up on the way there, what kVA a transformer is asked to carry, what a generator has to start, and what the power factor is.
Conduit Fill Calculator
Conduit fill calculator for EMT, IMC, RMC, PVC, FMC, and LFMC. NEC Chapter 9 fill percents, with the minimum trade size.
Voltage Drop Calculator
Voltage drop calculator for copper or aluminum, single or three phase. The 3% and 5% figures are NEC informational notes.
Wire Size Calculator
Wire size calculator from NEC 2023 Table 310.16 at 75°C, plus a voltage-drop check. Verify with local code and an electrician.
Watts, Amps, and Volts Calculator
Amp calculator for watts, amps, and volts. Single phase or three phase, with power factor and apparent power.
Box Fill Calculator
Box fill calculator using NEC 2023 314.16 volume allowances and metal box volumes. Verify with local code.
Recessed Lighting Calculator
Recessed lighting calculator. Spacing from ceiling height, plus a lumens target from foot-candles by room type.
Transformer Calculator
Transformer calculator for kVA, full-load amps, and the next standard size. Single-phase and three-phase. Planning only.
Generator Size Calculator
Generator size from running watts and the largest starting surge. Nameplates win. No transfer-switch sizing.
Power Factor Calculator
Power factor, kilovars, and the capacitor kilovars to reach a target. Planning only. No protection sizing.
How these calculators work
Wire size starts at the 75°C column of NEC 2023 Table 310.16, copper or aluminum. Ambient and bundling factors stay at 1 unless you enter them. A second size respects 240.4(D), which caps 14, 12, and 10 AWG even when the table ampacity is higher. Voltage drop reuses the Chapter 9 K method and names a size at or under 3%. That 3% is an informational note, not a rule that fails an inspection. Verify the result with the adopted code and an electrician.
Conduit fill uses Chapter 9 Table 1: 53% for one conductor, 31% for two, 40% for three or more, and 60% for a nipple 24 inches or shorter. Conductor areas are Table 5. Conduit areas are the 100% column of Table 4. When every wire is the same size, a fractional count of 0.8 or more rounds up, which is Note 7. Derating and box fill are separate problems.
Voltage drop is 2 × K × amps × one-way feet ÷ circular mils for single phase, and √3 instead of 2 for three phase. K is 12.9 for copper and 21.2 for aluminum. The 3% branch and 5% feeder figures are informational notes in 210.19(A) and 215.2(A). The amp calculator is the power identity those amps come from: volts × amps × power factor, or √3 for three phase. The transformer page uses that same √3 for full-load current from kVA. It does not select overcurrent protection. The generator page adds running watts and one motor surge. The power factor page is kW divided by kVA, and the kilovars to close the gap. Neither page sizes a conductor.
Box fill follows NEC 2023 314.16(B) and the metal-box volumes in Table 314.16(A). Each conductor counts once, grounds count as one, clamps count as one, and each device yoke counts as two. The result says whether the count is under the tabulated volume. It does not say the box is safe. Recessed lighting uses a spacing rule of thumb, ceiling height apart, plus a foot-candle target by room. Those foot-candle numbers are published summaries, not the IES selector.