Cable sizer, voltage drop and fillElectrician Calculator
Electrician Calculator is a pocket calculator for electricians who work to BS 7671 (UK) or NEC (US). Pick your region once, then size cables and check runs on site. Every result shows its working, and you can share it or save it to a job.
Every calculator is free. A one-time Pro unlock adds an unlimited cable sizer, every saved result grouped by job, and PDF job reports.
What it does
- Cable sizer: the smallest cable that passes current capacity and voltage drop, for BS 7671 and NEC
- UK voltage drop from Table 4D1B, with lighting (3%) and other uses (5%) limits
- UK cable derating and current capacity from Table 4D1A with Ca, Cg and Ci
- NEC wire ampacity with terminal ratings and 240.4(D) small conductor limits
- NEC conduit fill and box fill
- Every result shows its working. Share it, or save it to a job
- Works offline, no account, and your results stay on your phone
Articles
Questions
Is Electrician Calculator free?
Yes. Every calculator is free. A one-time Pro unlock adds an unlimited cable sizer (the free version includes 3 sizes), every saved result grouped by job, and PDF job reports.
Which standards does it use?
UK mode is labelled to BS 7671:2018+A4:2026 and uses the Appendix 4 tables 4D1A and 4D1B. US mode uses the NEC (labelled NEC 2020): Table 310.16 with its correction and adjustment factors, and the K-factor method for voltage drop.
What does the cable sizer check?
For BS 7671 it finds the smallest cable where Iz covers In, after Ca, Cg and Ci, and voltage drop stays within 3% for lighting or 5% for other uses. For the NEC it checks the terminal column, the adjusted ampacity, the breaker (including 240.4(B) and 240.4(D)) and 3% voltage drop. Each check is shown with its numbers.
What does it leave out?
UK conduit fill, 90°C thermosetting and aluminium Iz, twin and earth tables and earth fault loop impedance are left out rather than guessed. Use the IET On-Site Guide and the full standards alongside the app.
I bought Remove Ads before. Do I get Pro?
Yes. Open More, then Electrician Calculator Pro, and tap Restore purchase. Your earlier purchase unlocks Pro at no extra cost.
Get Electrician Calculator
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