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About FieldCalc

Free field engineering calculators for the people who build and maintain the world — electricians, HVAC technicians, engineers, apprentices, and DIYers.

What we do

FieldCalc is a free set of five code-cited calculators: conduit fill, wire size and ampacity, voltage drop, duct sizing, and beam deflection. Every tool runs entirely in your browser — no signup, no paywall. Install it once and it keeps calculating with zero signal, because the whole site is an offline-capable PWA designed for basements, attics, rooftops, and remote job sites.

How we build answers you can defend

Each result names the exact code table or formula behind it, so you can check the method, learn the code, and defend the number to an inspector:

Electrical

NEC 2023 — Chapter 9 fill, Table 310.16 ampacity, Tables 8/9 impedance, Table 250.122 grounding.

HVAC

ACCA Manual D equal-friction method for round, rectangular, oval, and flex duct.

Structural

IBC Table 1604.3 deflection limits with Euler-Bernoulli beam theory.

How we verify every number

A calculator is only as trustworthy as its tables and its tests. Our verification runs in four layers:

Primary sources only. Electrical data comes from NFPA 70 (NEC 2023) tables — Chapter 9 fill, 310.16 ampacity, 310.15 correction, 250.122 grounding. Duct math follows ACCA Manual D and ASHRAE fundamentals. Beam checks use IBC Table 1604.3 with closed-form Euler-Bernoulli solutions. Unit conversions use NIST SP 811, ASTM B258, and IEC 60228. Every page names its source.
Cross-reference against published answers. Conduit results are checked against NEC Annex C maximums. Wire ampacity is checked against manufacturer tables at base conditions. Duct sizes are checked against Manual D friction charts. Any disagreement is investigated before it ships — and borderline cells round conservative.
Automated math tests. Every formula in the calculation library carries unit tests with known reference values (142 tests and counting) that run on every build. If a table edit breaks a single value, the build catches it before users do.
Worked examples you can audit. Each guide walks a real scenario with every intermediate number shown — base ampacity, correction factors, terminal caps — so you can reproduce the result by hand and trust the method, not just the output.

Tables are reviewed within 90 days of newly adopted code editions. Found a number that looks wrong? Send the inputs and your code edition via our contact page — calculation disputes get priority.

Who uses FieldCalc

Journeyman electricians running fast field checks on pulls, breakers, and long feeders.
Apprentices studying for licensing exams, learning the NEC from cited tables.
HVAC installers sizing branches and trunks room-by-room from Manual J loads.
Contractors, DIY homeowners, and engineering students verifying bids and homework.

Our principles

Free forever. Every calculator, every guide — no locked features.
Private by design. No accounts; we use Google Analytics for aggregate usage stats only — your calculation inputs never leave your device.
Offline first. If it doesn't work in a basement with no bars, it doesn't ship.
Show your work. Inputs, formulas, and code references on every result — printable to PDF.

A note on responsibility

FieldCalc is a field aid, not a substitute for the code edition your jurisdiction enforces or for licensed professional judgment. Always verify against your local amendments. See our terms & conditions for the full disclaimer.

Get in touch

Found a bug, want a feature, or need a table checked? Head to our contact page — we read everything.