Electrical & low-voltage calculators
Field math,
done right.
Voltage drop, box fill, conduit fill, ampacity, PoE — eight calculators with verified formulas and answers you can read from a ladder. No ads, no subscription, works in a basement with no signal.
Why this app exists
The shelf is full of calculators
that get the math wrong.
Read the reviews of the top electrical calculators: results “very far off from being correct”, ads that lock you out mid-calculation, features pulled into subscriptions, reference apps where finding a table takes longer than walking to the truck. An electrician's calculator has one job — being right — and it's the one thing the shelf keeps failing at.
Answers you can defend
Every formula is tested against published worked examples and cross-checked with industry calculators. When the top apps on the shelf get voltage drop wrong, accuracy is the product.
Box fill that actually exists
The calculator the field keeps asking for: conductors, grounds, clamps, devices — NEC 314.16(B) method with a full line-by-line breakdown and the smallest standard box that fits.
Low-voltage & datacom included
PoE budgets by class (af/at/bt), Ethernet run limits, DC drop for cameras and LED runs at 12/24/48V. One app for the electrician and the low-voltage tech.
Big answers, live
The result updates as you type, in numbers you can read from a ladder. Green when you're within limits, red with the reason when you're not.
Remembers your inputs
Every calculator reopens with your last values — because real work is a series of similar runs, not one-off math.
Offline, no ads, no nagging
No ads popping mid-calculation, no rate-me loops, no account. It works in a basement with no signal — where the work actually is.
Built for the field
Advisory by design. Honest about it.
AmpCalc shows its work: the ampacity screen lists every step — base value, temperature correction, bundling adjustment, termination limit, breaker cap — so you can verify each one. Where the method has limits (large conductors, exotic conditions), the app narrows its scope instead of guessing. Always verify against the current NEC and local amendments.
More from VaultLabs for pros: JobQuote — estimates signed on the spot · JobProof — jobsite documentation.
- Nothing leaves your phone. No server, no account, no analytics — your records live on-device and export to your own iCloud Drive or Files.
- Yours, even if we disappear. Cloud tools get shut down and take your data with them. A local-first app can't be switched off from a server — your records stay files you control.
- Paid once. One-time purchase. No subscription, no upsell, updates included.
FAQ
Questions
Which calculators are included?
Voltage drop (with minimum-wire-size mode), box fill, conduit fill, wire size / ampacity with derating, Ohm's law & power (single- and three-phase), PoE budget, Ethernet cable run limit, and DC low-voltage drop. Free tier includes three; one purchase unlocks all of them forever.
How do I know the math is right?
Every formula runs against a suite of published worked examples from industry and trade-education sources, and results are cross-checked with widely used manufacturer calculators. Where an official chart differs from pure math by a wire, we stay on the conservative side — and say so.
Does it replace the NEC?
No. AmpCalc is a reference and educational tool built on standard formulas and NEC methodology. Always verify against the current code and local amendments — the app reminds you of that too. NEC is a registered trademark of the NFPA; AmpCalc is not affiliated with the NFPA.
Does it work offline?
Completely. No account, no server, no analytics. Your inputs stay on your phone.
Is it really a one-time purchase?
Yes. $9.99 once, yours forever, all 8 calculators. No subscription. All future updates are included — you always run the latest version at no extra cost.
