Field engineering calculators for NEC, HVAC & structural work

FieldCalc is a free set of field engineering calculators for electricians, HVAC technicians, structural engineers, apprentices, and anyone who needs a code-cited answer fast. Every tool runs entirely in your browser: there is no signup, no tracking, and 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. Each result shows the exact code table or formula it came from, so you can check the method, learn the code, and defend the number to an inspector. When the math is settled, copy a shareable link for the crew or save a clean print/PDF report for the permit folder.

Electrical calculators, per NEC 2023

Three of the five tools cover everyday electrical work under the National Electrical Code, 2023 edition. The conduit fill calculator checks EMT, PVC, RMC, IMC, and flexible conduit against NEC Chapter 9 Table 1 limits — 53% for a single conductor, 31% for two, 40% for three or more, and 60% for short nipples — using real Table 4 conduit areas and Tables 5/8 conductor areas. It flags risky jam ratios between 2.8 and 3.2, auto-sizes equipment grounding conductors per Table 250.122, and finds the smallest legal trade size for mixed wire pulls. The wire size and ampacity calculator sizes copper and aluminum conductors per Table 310.16, then applies temperature correction, bundling derating for 4+ conductors, 110.14(C) terminal-temperature caps, and 240.4(D) small-conductor breaker limits, with parallel runs per 310.10(H). The voltage drop calculator checks the NEC 3% branch / 5% total guidance for DC, single-phase, and three-phase runs, finds minimum wire size or maximum distance, and offers an Advanced Table 9 mode with power factor and conduit type for motors, steel raceways, and large feeders. Browse all three in the electrical calculators collection.

HVAC duct sizing, per ACCA Manual D

The duct sizing calculator applies the ACCA Manual D equal-friction method to residential and light-commercial ductwork. Enter CFM directly or derive it from tonnage and room loads, pick a friction rate (0.08 in.wg/100 ft is the residential standard; 0.06 for quiet bedrooms, 0.10 for short trunks), and get round, rectangular, oval, and flex sizes in one pass. Rectangular equivalents use the Huebscher equation for equal friction — never raw area — with aspect ratios capped at 4:1. Built-in CFM helpers, a TEL-based friction-rate finder, altitude correction to 10,000 ft, and velocity/noise checks keep branches in the quiet 600–900 FPM band and returns at 400–600 FPM. A CFM-to-size chart and step-by-step sizing guide sit one click away in the HVAC calculators section for quick lookups.

Beam deflection, per IBC limits

The beam deflection calculator covers simply supported, cantilever, fixed-fixed, and propped beams under point, uniform, and moment loads, with combined loading via superposition. Enter span, stiffness (E from material presets like steel, aluminum, and SPF wood; I direct or from the built-in rectangular/circular section helper), and loads to get maximum deflection with its location, reactions, shear and moment values, bending stress, and live deflection, moment, and shear diagrams. Every result is checked against IBC Table 1604.3 serviceability limits — L/360 for floor live load, L/240 total, L/480 for tile and brittle finishes, L/180 for cantilevers — in both SI and Imperial units. Find it alongside its formula reference and allowable-deflection chart in the structural calculators collection.

Who uses FieldCalc

Journeyman electricians use FieldCalc for fast field checks on conduit pulls, breaker sizing, and long feeder runs. Apprentices studying for licensing exams use the worked examples and cited tables to learn the NEC instead of memorizing it. HVAC installers size branches and trunks room-by-room from Manual J loads. General contractors and DIY homeowners sanity-check bids and subpanel feeds. Engineering students verify homework against closed-form formulas with every variable shown. If you work with wire, air, or beams, these construction calculators speak your language: amps and circular mils, CFM and friction rate, spans and span ratios.

Offline, shareable, and printable

FieldCalc is engineered for places with no bars on the phone. A service worker caches every page and calculator, so the tools load and compute fully offline after the first visit, and the app installs to your home screen like a native tool. Every calculation encodes its inputs into the URL, so a result is a link you can text to a foreman, bookmark for later, or attach to a work order — no screenshots, no retyping. A print stylesheet strips navigation and interactive chrome to produce a one-page report with inputs, results, and code references, ready to Save as PDF for inspectors, customers, or your own records. Because all math runs on-device, your job data never leaves your phone.

How to use the calculators

Pick a tool from the grid above, enter your values in plain field units, and read the verdict instantly — every keystroke recalculates. Green means pass, red means fail with the reason named: wrong fill limit, failed derating, excessive drop, noisy velocity, or exceeded deflection. Adjust one input at a time to see what drives the result, then share the link or print the page. Start with conduit fill for raceway planning, wire size for breaker and conductor selection, voltage drop for long runs, duct sizing for airflow, and beam deflection for sag checks.