Why we publish this
A calculator site that never finds an error isn’t checking.
All of the entries below came out of our own audits and test suite. Found the next one? Use the contact page and it’ll end up here with a date.
August 2026
Two internal audits ran in August 2026. One recomputed every formula against primary sources. The other checked every product, size and term against the North American market. Below are the confirmed errors, and roughly what each one would’ve cost you.
- Aug 8 (Gravel): The calculator computed the in-place volume, labeled it loose and told you to order that. Under-ordered by the compaction factor. Now orders the loose volume for your finished depth.
- Aug 9 (BTU): Replaced the flat 20 BTU per sq ft rule with the ENERGY STAR sizing table. The flat rule undersized small rooms by up to 40% and oversized large spaces by a similar margin.
- Aug 9 (Tile): Thin-set was a flat 85 sq ft per 50 lb bag regardless of tile size. Large-format tile on a 1/2 in notch under-ordered mortar by roughly 60%. Coverage now follows the notch the tile size forces.
- Aug 9 (Pavers): Gravel base was figured on the paved area instead of the excavation, about 19% short. The dig extends past the pavers so the edge restraint bears on compacted stone.
- Aug 9 (Gravel): Road base carried its compacted-in-place density on top of a separate compaction allowance, so the same compaction counted twice. Roughly 10% over.
- Aug 9 (Insulation): A single R-19 entry carried the 23 in roll coverage, so jobs framed at 16 in on center under-ordered by 35%. Split by stud spacing. R-49 blown corrected to 39.9 sq ft per bag, and R-23 mineral wool corrected from 47.8 to 39.8.
- Aug 9 (Epoxy): The tool added primer gallons to base-coat gallons and rounded the sum (one figure for two products bought separately), and it left out the clear topcoat entirely. Each product now rounds up on its own.
- Aug 9 (Fence and post hole): Post depth was a flat 24 in minimum for every climate, which is above the frost line across the northern US and nearly all of Canada. Depth is now driven by your local frost line.
- Aug 9 (Asphalt and retaining wall): Tonnage rows were labeled with a bare t (the symbol for the metric tonne) while computing US short tons. A silent 10% error for anyone buying by the tonne. Now labeled tons, with the basis stated.
- Aug 9 (Stairs): The code check ignored the editable max-riser field and was hardwired to the IRC, so it failed legal Canadian stairs. It now honors the field and offers both IRC and NBC limits.
- Aug 9 (Sod): A FAQ said a 450 sq ft pallet holds around 60 rolls of 10 sq ft sod. That works out to 600 sq ft. Corrected to 45.
- Aug 22 (This site): The methodology page briefly cited a superseded thin-set rate and overstated its own test count (147, where the correct figure that day was 145). Corrected the same day. The count is now stated as a floor so it can’t drift.