Where do your numbers come from?

Geometry, published bag yields, standard material unit weights and derived steel properties — all computed in your browser. We do not reproduce copyrighted code or specification tables.

Are these calculators code compliant?

They give quantities, not designs. Slab thickness, footing depth, reinforcement and wall heights are governed by the building code adopted where you build. Confirm those with your building department or a licensed professional.

How our numbers are calculated

Every figure on CementCalc is derived from geometry, a published nominal yield, or a standard material unit weight. Here is each one, and its limits.

Quick answer

We calculate volumes from geometry, convert with exact definitional factors (27 cubic feet per cubic yard), and weight with standard unit weights — 150 lb/ft³ for concrete, 100 to 135 lb/ft³ for aggregate. Bag counts use manufacturers' published yields. No copyrighted code or specification table is reproduced anywhere on this site.

Constants and where they come from

Value	Used for	Basis
27 ft³ = 1 yd³	Every volume conversion	Definitional (3 x 3 x 3 ft)
150 lb/ft³	Concrete weight, 4,050 lb per yard	Standard unit weight of normal-weight concrete
0.60 / 0.45 / 0.375 / 0.30 ft³	80 / 60 / 50 / 40 lb bag yields	Nominal yields published by US bagged-mix manufacturers
0.2836 lb/in³	Rebar weight per foot	Density of steel; weight = area x 12 in x density
bar no. / 8 in	Rebar diameter and area	US bar designation is diameter in eighths of an inch
100–135 lb/ft³	Gravel, stone and sand tonnage	Typical loose unit weights; labelled as estimates
1 : 2 : 3 through 1 : 3 : 6	Mix ratio chart	Long-standing nominal volumetric site mixes
40 bar diameters	Lap splice rule of thumb	Common residential practice, not a code value

Every constant used by the calculators, with its basis.

What we do not do

We do not reproduce tables from the building code, ACI documents or ASTM standards. Those are copyrighted, and copying them would be both unlawful and misleading — a table lifted out of its standard loses the conditions that make it valid. Where a value comes from a standard, we derive it from the underlying geometry or physical constant and say so.

We also do not give structural designs. A calculator can tell you that a footing of a given size holds 1.2 cubic yards; it cannot tell you that the footing is the right size for your soil, frost depth and load. That is a building department and engineering question, and every calculator on the site says so.

Cost defaults are typical US ranges and are fully editable. They are a planning budget, not a quote — ready-mix pricing moves with fuel, haul distance and season.

Corrections

If a figure here looks wrong, it matters — quantities that are off cost real money on a pour day. Every calculation runs client-side and the formula for each result is printed on its page so you can check the arithmetic yourself.

Constants and where they come from

What we do not do

Corrections

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