How we calculate
Methodology: Every Formula Shown, Every Result Rounded Up
A calculator you can't check is just an opinion with buttons. This page documents exactly how HowMuchBuild calculators work — the constants we use, where they come from, and the rules every result follows.
By HowMuchBuild Editorial TeamCalculation reviewedUpdated October 2026
How the calculators work
Every calculator on this site follows the same pipeline: your dimensions go in, standard geometry converts them to a volume or area, published material constants convert that into quantities, and a waste or allowance factor adjusts for the real world. The calculation steps are displayed on the results panel of every tool, so you can verify the arithmetic yourself — bring your own calculator and check us.
All math runs in your browser (client-side). Nothing you enter is sent to a server, stored, or tracked.
Published constants we use
We use standard, verifiable figures — never guesses. The core constants:
| Constant | Value | Basis |
|---|---|---|
| Cubic feet per cubic yard | 27 (exact) | Definition: 3 ft × 3 ft × 3 ft |
| 80-lb premix bag yield | 0.60 cu ft | Manufacturer-published (e.g. Quikrete, Sakrete packaging) |
| 60-lb premix bag yield | 0.45 cu ft | Manufacturer-published packaging |
| 40-lb premix bag yield | 0.30 cu ft | Manufacturer-published packaging |
| Nominal 4×4 post, actual | 3.5″ × 3.5″ | US dressed lumber standard |
| Nominal 6×6 post, actual | 5.5″ × 5.5″ | US dressed lumber standard |
Weight conversions (gravel tons, sand tons) are presented as ranges, because bulk density genuinely varies by material type and moisture. Where a figure is an estimate rather than an exact conversion, the page says so.
Rounding-up policy
Bags, boards, sheets, tiles, and boxes are always rounded up — you cannot buy a fraction of a bag, and running short mid-project is the expensive failure mode. Volumes in cubic yards or cubic feet are shown to two decimals for ordering from bulk suppliers, who sell fractional yards.
Cost estimates
Cost figures follow strict honesty rules:
- We never invent prices. Cost estimator inputs start empty — you enter your local store's prices.
- Every cost is labeled an estimate, with a note that prices vary by store and region.
- Cost guides cite ranges, never precise figures, and always note that actual prices vary widely by region, site conditions, and finish level.
Review process
Every calculator is reviewed by the HowMuchBuild editorial team before publishing: the formulas are checked against the documented constants, the worked examples are recomputed by hand, and edge cases (zero inputs, extreme values) are tested. Pages are re-reviewed when updated — the “Updated” date on each page reflects its last review.
Limitations
- Results are planning estimates, not quotes and not engineering or professional advice.
- Real projects have irregular shapes, uneven ground, and waste beyond any allowance — the calculators model the ideal case plus a configurable margin.
- For structural work, permits, or anything load-bearing, consult a licensed professional in your area.
Questions about our math? Contact us — we'd rather fix an error than defend one.