Voltproof: Electrician Calc

⚡ The electrician calculator that shows its work. No ads. No account. Works offline.

Voltproof gives you the answer and the proof. Every result shows the formula, your own numbers plugged into it, and the NEC article the rule comes from, so you can check it, learn from it, and hand it to an inspector.

🔧 13 CALCULATORS
• Voltage drop calculator: single and three phase, copper or aluminum, drop in volts and percent, plus the longest run that stays under your limit
• Wire size & ampacity calculator: 60/75/90 °C insulation and terminal rating, ambient temperature, current-carrying conductors, continuous loads and parallel sets
• Conduit fill calculator: EMT, IMC, RMC, PVC Schedule 40 and 80, ENT, FMC and LFMC
• Box fill calculator: conductors, clamps, devices and grounds
• Breaker size calculator
• Ground wire (EGC) size
• Residential load calculation and service size (standard method)
• Motor FLA and branch circuit
• Transformer sizing
• Ohm's law
• Watts to amps, amps to watts, kW, kVA and HP
• Resistor color code
• Unit converter: wire size, length, temperature, energy and more

📐 SEE THE WORK
Formula, then your numbers, then the result, with a clear pass or fail. Go over a 3 % voltage drop and the meter turns amber and suggests the next wire size up. Conduit fill draws your actual wires inside the pipe.

💬 ASK IN PLAIN WORDS
Type "wire for 50 A, 120 ft, 240 V" and the right calculator opens, already filled in. It runs on your phone.

📚 REFERENCE TABLES
IP ratings, NEMA enclosure types, conductor colors, trip curves, RCD types, earthing systems, mains voltage and plugs by country, EV connectors, RJ-45 wiring and SI prefixes.

🛠 BUILT FOR THE JOB SITE
Works with no signal. Dark mode. Favorites. A home-screen widget and a quick-settings tile open your go-to calculator in one tap. Feet or meters, your choice.

⭐ VOLTPROOF PRO — buy once, or pay yearly
• Unlimited jobs: keep every calculation for a job in one place
• PDF reports with your name on them, ready for an inspector or a client
• Scan a nameplate: point the camera at a motor or transformer plate and the values fill in for you
• NEC 2020 and NEC 2026 alongside NEC 2023
• 500 results of history (the free app keeps 20)
• Back up and restore your jobs to a file

Pro is unlocked on your phone, so it works offline and restores by itself on any phone signed in to the same Google account. No licence server, no login.

FREE, FOREVER: all 13 calculators with full worked solutions, one job, your last 20 results, the reference tables, the widget and the tile.

For electricians, apprentices, electrical engineers, solar and EV charger installers, and serious DIYers.

⚠️ Voltproof is a calculation aid. Always check results against the code edition adopted where you work and with your Authority Having Jurisdiction. NEC® and NFPA 70® are registered trademarks of the National Fire Protection Association. Voltproof is not affiliated with or endorsed by NFPA.