Builder Calc is a free collection of construction calculators and quick-reference tools built for builders, contractors, and tradespeople. Every tool runs entirely in your browser — no sign-up, no ads, and no data leaves your device.
Whether you are framing walls, pouring a concrete slab, laying tile, or estimating materials for a bid, these calculators help you get accurate numbers fast. Use the Foundation Square calculator to check 90-degree corners with the 3-4-5 method, figure stair rise and run to meet IRC code, or size rafters by pitch and span. The Concrete Calculator tells you how many cubic yards — and how many 60 lb or 80 lb bags — you need for slabs, footings, and cylindrical piers.
For estimating jobs, the Area Calculator supports rectangles, triangles, circles, and more with live SVG previews. The Flooring and Tile calculator figures square footage and piece count with a configurable waste allowance, while the Paint Calculator works out how many gallons you need after deducting doors and windows. Mulch, gravel, and topsoil volumes are covered too — in cubic yards and bag counts.
On the math side you will find a fraction-to-decimal converter, a right-triangle solver, percentage calculations, ratio and proportion solving, and a full unit converter that handles length, weight, volume, temperature, and more. Electrical calculators cover Ohm's Law, resistor and capacitor values, voltage dividers, LED resistor sizing, and power-cost estimates.
Business and job-site tools include a weekly time card with overtime and gross-pay calculations, a markup-vs-margin converter, and a line-item material cost estimator with tax. Specialty calculators round out the set with pipe and cylinder volume in gallons, liters, and cubic feet, plus BTU and room-sizing estimates based on square footage, insulation quality, and climate zone.
All tools are mobile-friendly, work offline once loaded, and support dark mode. Bookmark the ones you use most and keep them one tap away on the job site.