Fifteen free, browser-only calculators for electricians, contractors, and homeowners. Every tool runs entirely in your browser — nothing is sent to a server, no signup required, and no ads inside the calculator. Each tool links to the relevant code reference so you can verify the result yourself.

Electrical Code Calculators

• NEC Wire Size Calculator — Size copper or aluminum conductors by ampacity and voltage drop using NEC Table 310.16 and Table 310.12.
• Voltage Drop Calculator — Verify drop is inside the NEC 210.19(A) targets: 3% on branch circuits, 5% total feeder plus branch.
• Electrical Load Calculator (NEC 220) — Size a residential service using the NEC 220 standard method. Returns total VA, amps, and the next standard service size.
• Conduit Fill Calculator — Check EMT, IMC, RMC, and PVC Schedule 40/80 fill against NEC Chapter 9 Table 1 limits (40% for 3+ conductors).
• Box Fill Calculator (NEC 314.16) — Sum conductor, device, clamp, and EGC allowances and compare to the listed box volume.
• Motor FLA & Branch Circuit Calculator — Pull FLA from NEC Tables 430.247-250, apply the 125% branch-circuit factor per NEC 430.22.
• Grounding Conductor Sizer — Size the GEC (NEC Table 250.66) or EGC (NEC Table 250.122). Copper and aluminum.
• Ampacity Derating Calculator — Apply ambient temperature, conductor bundling, and termination temperature limits per NEC 310.15.
• Conduit Offset Calculator — Bend marks, shrink, and travel for parallel offsets in EMT and rigid conduit.

Construction Estimating Tools

• Concrete Volume Calculator — Cubic yards and 80 lb bag count for slabs, footings, and round columns. Includes configurable waste allowance.
• Drywall, Mud & Tape Estimator — Sheet count, mud weight, tape footage, and screw count per room for 4×8, 4×10, and 4×12 sheets.
• Roofing Material Estimator — Roof squares, shingle bundles, underlayment rolls, and ridge cap linear feet from footprint plus pitch.
• Construction Markup Calculator — Convert margin to markup (and back), add overhead and profit, and see the full bid breakdown.
• Construction Unit Converter — Length, area, volume, lumber board feet, and AWG to mm2. All conversions auto-update as you type.
• Stair Stringer Calculator — Rise, run, stringer length, and stair count to IRC R311.7 limits. Flags non-conforming combinations.
• Solar Panel Payback Calculator — Simple payback period, lifetime production, and lifetime savings for a residential PV system.

Need the NEC article behind a result? Visit the NEC Code Lookup Hub for article-by-article quick reference, or read How to Read the NEC Codebook Online (Free, Legally).

Stuck in coordination instead of conduit math? See the BIM Clash Audit — fixed-price federated-model review for GCs and trade contractors.