Editorial Standards
Every number a calculator on this site produces traces back to a manufacturer figure or a documented, checkable formula — not a guess.
Where our constants come from
Bag yields — how many cubic feet of placed concrete come out of a 50, 60, or 80 lb bag — are taken from manufacturer packaging and technical data sheets, not estimated from mixing experience. We use 0.375 cubic feet for a 50 lb bag, 0.45 for a 60 lb bag, and 0.60 for an 80 lb bag, consistent with the major national concrete mix brands.
Material densities — tons per cubic yard for gravel, sand, crushed stone, topsoil and similar materials — are typical dry bulk density values drawn from aggregate industry references. Actual density varies with moisture content, particle size, and compaction, so these are representative figures rather than a guarantee for any specific quarry's product.
Concrete block dimensions and weights follow standard nominal CMU sizing (8×8×16 and its common variants), using typical published weights for normal-weight block. Lightweight and aerated block weigh meaningfully less; we note that wherever it's relevant.
How the formulas work
The underlying math is standard geometry — the volume of a rectangular prism for slabs and footings, a cylinder for sonotubes and post holes, minus the post's own volume where relevant. There's no proprietary adjustment or fudge factor beyond the waste percentage, which is a separate, clearly labeled input you can change or zero out.
Reference tables
The example tables on each calculator page are computed by running the same formula the live calculator uses against a fixed set of inputs, then pasting the results — not calculated separately by hand. This keeps the table and the interactive calculator from silently drifting apart.
Corrections
If a figure here doesn't match what you're seeing on a bag, a spec sheet, or a supplier's quote, we want to know. Reach us through the contact page with the calculator, the input, and what you found instead. We review and correct errors rather than leaving them in place.
What we don't cover
These calculators don't account for local code requirements, soil-bearing capacity, seismic or wind loading, or site-specific engineering. Where a project is structural or permitted, our numbers are a starting point for a conversation with a licensed professional, not a substitute for one — see our disclaimer.