DC Electrical Calc: Wire Size

Wire sizing, voltage drop and ampacity for 12 V, 24 V and 48 V DC systems — offline, on site. Choosing a conductor means satisfying three rules at the same time: voltage drop, ampacity, and the small-conductor overcurrent limits in NEC 240.4(D). Most calculators check one of them and stop. Enter the current, the one-way distance and the system voltage. DC Electrical Calc returns the smallest conductor that satisfies all three at once, then tells you in one sentence which rule is actually limiting the answer: "Limited by voltage drop — not by ampacity. A smaller conductor would carry this current, but its drop would exceed the limit you set." When no size satisfies the constraints it says so, instead of returning the nearest one. Where the underlying table has no published value — 18 AWG and 16 AWG copper at 75 °C, for example — those sizes are treated as failing rather than guessed at. EIGHT TOOLS • Wire Sizing — the smallest conductor that passes drop, ampacity and 240.4(D) together • Voltage Drop — forward calculation for a size you already have • Fuse & Breaker — protective device rating, checked against the conductor • Ohm’s Law & Power — fill in any two of volts, amps and ohms • Battery Bank — series and parallel cells into one bank: voltage, capacity and energy • Inverter Sizing — continuous and surge watts to compare against a nameplate • Runtime — how long the bank lasts at a given load • Ampacity Tables — NEC 310.16 copper and aluminium at 60 °C, 75 °C and 90 °C, plus conductor areas and circular mils EVERY ANSWER SHOWS ITS WORK Tap "Show working" on any result and the formula appears with the values already substituted, so the answer can be checked by hand or handed to an inspector. Nothing is a black box. BUILT FOR THE PLACES YOU WORK • Free, with no in-app purchases, no subscription and no ads • No account and no sign-in • No network connection needed — it works in airplane mode • Metric and AWG in the same view; change units without re-entering anything • Light and dark themes WHAT IT DOES NOT DO It does not size AC circuits, it does not do load calculations for a whole installation, and it is not a substitute for the code book. SAFETY On first launch the app asks you to read a safety notice before it will let you continue. This is a calculation aid. Follow the electrical code that applies where you are installing — NEC for land installations, ABYC E-11 or the equivalent for marine work — and have the work verified by a licensed electrician or surveyor. The app does not constitute engineering advice, and responsibility for a selection rests with the person who makes it.