ABOUT

WHAT IS PROJECTCALC?

Built for real projects

ProjectCalc is a free library of fast, accurate calculators for construction, home improvement, and DIY projects. Whether you're estimating drywall for a remodel, sizing a circuit breaker for a new subpanel, or calculating pipe slope for a drain run — the math is already here.

Every calculator uses the same formulas and code references that professionals rely on: NEC for electrical, IPC for plumbing, ACCA for HVAC, IRC for structural. Results are meant for estimation and planning; always verify final specs with your local code and a licensed professional.

Who it's for

Contractors doing quick field estimates. Homeowners planning a weekend project. Students learning the trades. Anyone who needs a number fast and accurate without digging through a code book or firing up a spreadsheet.

What's here

Over 70 calculators across five trades — Carpentry, Masonry & Siding, Electrical, Plumbing, and HVAC — plus home & DIY categories (concrete, roofing, flooring, paint, insulation, and more) and basic finance tools. Each calculator page includes a plain-language FAQ and a link to the relevant code section where applicable.

The blog publishes practical guides on the same topics — how to read a load calculation, what pipe slope means for drain performance, when to upsize a wire gauge.

Methodology & sources

Calculator formulas come from current code editions and industry references, not blog posts:

  • Electrical — National Electrical Code (NEC) for voltage drop (Hazen-Williams not applicable; we use the standard K=12.9 copper resistivity), conduit fill (NEC Chapter 9), wire gauge ampacity (Table 310.16, 75°C terminations), panel load (NEC 220 Part III standard method), and circuit breaker sizing (NEC 240.6 + 210.20(A)).
  • Plumbing — International Plumbing Code (IPC) for drain pipe sizing (Table 710.1), vent sizing (Table 906.1), trap sizing (Table 1002.1), and fixture units. Hazen-Williams for friction loss with material-specific C-factors.
  • HVAC— ACCA Manual J approach for whole-home cooling/heating loads (with Heat Transfer Multipliers by IECC climate zone), CFM = BTU ÷ (1.08 × ΔT) for duct sizing, ASHRAE 62.2 for ventilation rates, EPA Section 608 references for refrigerant.
  • Carpentry — IRC R602.7 for header sizing (simplified residential ranges), AWC Maximum Spans for floor joists and rafters, NDS allowable stresses for built-up beams. ASCE 7 simplified for snow loads.
  • Masonry— Brick Industry Association (BIA) for modular brick math (6.86 bricks/ft² with 3/8" joint), ACI 318 for rebar cover requirements, manufacturer spec sheets for stone veneer and stucco coverage.
  • Finance— Standard amortization formula (M = P·r(1+r)n ÷ ((1+r)n−1)) for mortgages, car loans, and personal loans. No proprietary modeling.

Where formulas have multiple acceptable approaches (e.g., several slope reduction equations for snow load), we use the simplest approach that produces results within 10% of the more complex methods, and document any deviation in the calculator's notes section.

Accuracy & limits

All calculators are estimating tools, not substitutes for engineered drawings, code-stamped tables, or licensed professional sign-off. Code editions evolve and local jurisdictions amend them — the math here is good for planning, ordering, and sanity-checking. For permit submittal, structural design, code compliance, or anything where being wrong has real consequences, defer to your local building department, licensed electrician, plumber, HVAC contractor, or structural engineer.

Structural and life-safety calculators (beam span, header size, stair stringer, snow load, panel load, etc.) carry an explicit “estimate only” disclaimer in the result row.

Updates

Calculator math is reviewed annually against the latest code cycle. Major changes (e.g., the 2026 IRS mileage rate, NEC code cycle updates) trigger faster updates. The blog publishes new project guides on a regular cadence; calculator additions ship as new use cases come up.

Pro Toolkits

For contractors who need a full estimating workflow, we sell Pro Toolkits on Etsy — trade-specific Excel workbooks covering takeoff, material pricing, and a client-ready quote sheet. Available for Roofing, HVAC, Plumbing, Framing, Electrical, and Concrete.

Who runs it

ProjectCalc is an independent site run by a solo developer based in the United States. It is funded by affiliate commissions and advertising — no subscriptions, no paywalls, no account required. Inputs to every calculator stay in your browser; nothing is sent to a server.

Contact

Feedback, corrections, or partnership inquiries — open an issue on the GitHub repository. Code corrections are especially welcome — if a calc disagrees with current code or a published source, file an issue with the citation and it gets fixed.