Field calculators that work the way you do

Punch in the job numbers, get the answer, get back to work. Fifteen free calculators for HVAC, electrical, concrete, and carpentry — built to be used one-handed on a phone at the job site.

AC BTU CalculatorSize a window unit, mini-split, or room AC in BTU and tons.Heating BTU CalculatorSize a furnace or heater by square footage and climate zone.Wire Size CalculatorRight AWG gauge for the amps and the distance — ampacity and voltage drop both checked.Voltage Drop CalculatorVolts and percent lost over a run — pass/fail against the 3% rule.Ohm’s Law CalculatorSolve volts, amps, ohms, and watts from any two values.Concrete CalculatorYards for the ready-mix order, bags if you’re mixing it yourself.Rebar CalculatorGrid layout, linear feet with laps, and 20-ft sticks to buy.Stair Stringer CalculatorRiser height, tread count, total run, stringer length — code-checked.Roof Pitch CalculatorDegrees, slope %, area multiplier, and rafter length from span.Wall Stud CalculatorStuds, plates, and lumber-yard board counts for any wall.Drywall CalculatorSheets, screws, mud buckets and tape for any room.Board Foot CalculatorConvert a cut list into board feet and dollars.Asphalt CalculatorHot-mix tons for a driveway or lot, with cost per ton.Excavation CalculatorBank yards, swelled loose yards, and dump-truck loads.Slope CalculatorConvert rise/run to percent, degrees, ratio, and inches per foot.

Why another calculator site?

Because most of them are ad-walls wrapped around a formula, built by people who have never loaded a truck at 5 a.m. Every tool here shows its math, states its assumptions, and gives you the buy-list numbers you actually order with — yards, bags, sheets, sticks — not just an abstract figure.

Everything runs in your browser. Nothing is stored, nothing requires an account, and every page loads fast on a weak jobsite signal.

Estimates, not engineering

These calculators use standard industry formulas and rules of thumb for planning and material takeoffs. They don't replace a Manual J for HVAC, the NEC for electrical work, or your local inspector for anything structural. When money or safety is on the line, the licensed professional and the local code always get the final word.