By Avery Schwartz — builder of ToolboxMath, AxleMath, and HouseMath.
I spent three years driving a truck for a living, and I built my first calculator site — AxleMath — because the scale math drivers run every day deserved a tool that showed its work. ToolboxMath is the same idea pointed at the trades: the fifteen calculations that come up on job sites over and over, done carefully, with the formula printed on the page.
Here's the honest part: I'm not a master electrician, an HVAC tech, or a general contractor, and this site never pretends otherwise. That's exactly why the math here doesn't come from me. It comes from the published sources the trades themselves use — NEC ampacity and voltage-drop math for the electrical tools, the IRC's 7¾-inch riser and 10-inch tread limits behind the stair calculator, standard ready-mix yardage practice for concrete, the 20-BTU-per-square-foot convention (and its limits) for AC sizing, and the board-foot formula lumber has been sold by for a century. Where a tool leans on a rule of thumb instead of a code table, the page says so out loud.
Every tool here follows three rules: show the formula, state the assumptions, and answer in the units you actually buy — yards, bags, sheets, sticks, tons. No signup, no app, nothing you type leaves your browser.
Where the estimate ends
These are planning and takeoff tools, not engineering. A wire-size answer here is a starting point that the National Electrical Code, your local amendments, and a licensed electrician get to finish. Stairs, footings, and anything structural belong to your local code official. The calculators are conservative on purpose, and every page carries the same warning where it matters.
Corrections
If a formula, assumption, or worked example on this site is wrong, I want to know more than you want to tell me. Send the calculator name and the inputs you used through the contact page — error reports jump the queue, and fixes ship fast.