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The voltage drop calculator that explains itself. No signup, no guessing.

🔥 Ampacity Check

Ampacity = the most current a wire can carry safely without overheating. Enter your wire and load, get a clear yes/no.

AWG = American Wire Gauge. It's printed on the wire jacket.

Not sure? Use 75°C — it's what most breaker and lug terminations are rated for. Romex/NM-B cable must use the 60°C column. THHN in dry locations is 90°C, but the connection points usually still limit you to 75°C.

amps

What this checks (and what it doesn't)

We look up your wire in the standard U.S. ampacity table (NEC Table 310.16 — normal conditions: up to three current-carrying wires in a conduit, ordinary room temperature). For small wires we also apply the special breaker-size rule (NEC 240.4(D)): 14 AWG copper tops out at a 15 A breaker, 12 AWG at 20 A, and 10 AWG at 30 A, even though the raw table says more.

Not included: hot attics/engine rooms, bundles of more than three current-carrying wires, and continuous loads (running 3+ hours straight needs 25% headroom). Those all reduce what the wire can carry — when in doubt, go up a size or ask an electrician.

Ampacity and voltage drop are separate checks — a wire must pass both.