Unit conversions

The internal volume basis is cubic feet. Length values convert using 1 ft = 0.3048 m and 1 in = 0.0254 m. Thickness in inches converts to feet by dividing by 12; metric thickness in centimetres converts to feet by dividing by 30.48.

Cubic yards are cubic feet divided by 27. Cubic metres use 1 ft³ = 0.028316846592 m³. Intermediate quantities retain full JavaScript numeric precision; displayed values are rounded for readability.

Geometry

A slab or rectangular footing uses length × width × thickness/depth. A wall uses length × height × thickness. A round form uses π × (diameter ÷ 2)² × depth. A round post hole with an optional round post uses the difference between the hole and post circle areas multiplied by concrete depth.

The post subtraction assumes the round post occupies the full entered concrete depth. Square posts, partial embedment, sloped forms, openings, and irregular excavation are not modeled by those simple formulas.

Allowance and purchasing rounding

The net volume is multiplied by the number of identical pours. The visitor-selected allowance percentage is applied to that net total: total = net × (1 + allowance ÷ 100). No allowance is presented as universally correct.

Bag counts divide the total volume by the entered mixed yield per bag and round up to whole bags. Ready-mix supplier increments are not automatically inferred by this calculator; use the rule in a supplier quotation.

Validation and limits

Dimensions must be positive and finite. Quantity is an integer from 1 to 10,000; allowance is from 0% to 100%. Post diameter must be nonnegative and smaller than the hole diameter. Out-of-range or incomplete inputs do not produce a result.

This code and its tests check quantities, not structural design, mix selection, strength, site conditions, or building-code compliance.

References