How We Build and Check Our Calculators
This page explains how every calculator on TallyBrix is built, checked and kept up to date.
1. Formulas come from standard practice
Each calculator uses the same geometry and unit conversions a contractor or supplier uses: area, volume, pitch factors, cubic yards and tons. Where a product figure matters (how much a bag of concrete yields, how many bricks fit in a square foot, how much a roll of underlayment covers) we use the figure printed by manufacturers or published by trade bodies, and we let you change it.
2. Every formula is checked by hand
Before a calculator goes live, its worked example is calculated by hand and compared with the tool. We also run automated tests that feed each calculator the worked example and check the answer, so a later change cannot quietly break a result.
3. Assumptions are visible and editable
Waste allowances, densities, bag yields and coverage figures are listed under Adjust assumptions on every calculator. They start at common values, and you can change any of them to match your product or supplier.
4. Rounding is done the safe way
Things you buy whole, such as bags, bundles, posts and boards, are always rounded up. Small floating-point errors are removed before rounding, so 24.0000001 bags is 24 bags, not 25.
5. Prices are yours
We never present a fixed national price as fact. Cost fields are filled in by you. If a page shows a reference price range, it shows the date and the source, and we review it every quarter.
6. We stay inside safe limits
Our calculators count materials and lay out geometry. They do not size structural parts, design footings or retaining walls, or give electrical, gas or plumbing instructions. Local building codes, permits and your supplier’s data always come first.
7. Corrections
If you think a number is wrong, tell us. We check every report. When we fix something, we note the date and the change on the calculator page.
8. Review dates
Every calculator shows the date its formulas and examples were last reviewed.