About & Method

What this site is

ConcreteCalc Guide offers free calculators for concrete volume, bags, weight, cost, reinforcement, mix ratios and related materials. It is an independent informational site, not affiliated with any concrete supplier or manufacturer. The calculators estimate quantities for planning and ordering; they do not design structures, set footing depths, choose reinforcement, or replace your local building code.

Nothing you enter is uploaded or stored: all calculations run in your browser. That is also why a result can be shared as a link — the measurements travel in the link itself, not through any server.

How the figures are calculated

Volume. Cubic feet = length × width × thickness, with all dimensions in feet (round shapes use π × radius² × thickness; stairs and footings use the stacked-block and cylinder formulas shown on their pages). Cubic yards = cubic feet ÷ 27. The order amount adds the waste allowance you choose.

Bag counts. Bag counts divide the order volume by the bag yield, rounded up. Yields are the published figures from QUIKRETE: an 80 lb bag yields about 0.60 cubic feet, 60 lb about 0.45, 50 lb about 0.375, and 40 lb about 0.30. That is why one cubic yard takes 45 × 80 lb bags, 60 × 60 lb bags, 72 × 50 lb bags, or 90 × 40 lb bags.

Weight. Typical weights used across the site: concrete about 4,050 lb per cubic yard (150 lb per cubic foot at normal density), gravel and dry sand about 2,700 lb per cubic yard, topsoil about 2,000 lb, and mulch about 400–800 lb depending on moisture. Lightweight concrete weighs less — check the mix density.

Mix ratios. The mix calculator multiplies the wet volume by the 1.54 dry-volume factor, splits the dry volume by the mix parts (M5 1:5:10 through M25 1:1:2), and converts the cement share to bags at about 1 cubic foot per 94 lb bag. Water starts from a 0.50 water–cement ratio by weight and must be adjusted for aggregate moisture and the slump needed — too much water weakens concrete.

Waste. The default waste allowance is 10% for formed work. Use 15–20% for hand-dug trenches and post holes, where the sides bulge and the hole is dug larger than the form.

Joints. Control-joint spacing follows industry guidance from NRMCA (Concrete in Practice CIP 6, Joints in Concrete Slabs on Grade): 24 to 36 times the slab thickness, capped at 15 ft, cut at least one-quarter of the thickness deep and at least 1 inch deep.

What the calculators do not decide

Slab thickness, footing depth and width, reinforcement spacing and size, concrete strength (PSI), wall thickness, and whether a design needs an engineer are structural decisions. The pages show typical residential practice reported by industry sources, clearly labelled as such, and always point to the local building code and, where required, an engineer’s design. Footing depth, in particular, must reach below the local frost line — the calculator cannot know your frost depth.

Costs. Price ranges are third-party reported figures for 2026, not quotes and not national fixed rates. They move with region, mix strength, access, finish and fuel surcharges. Always get a local quote before ordering, and ask about short-load fees, delivery minimums and pump charges.

How the site is checked

Every worked example and table figure on the site is recomputed from the same formulas the calculators use, and an automated harness re-runs the calculator logic against those examples. When a figure is corrected, the correction is checked on the live site before it is described as fixed. Figures are labelled with the date they were checked: this site was last updated on 29 October 2026.

Corrections and suggestions are welcome — if a figure on any page does not match its own worked example, it is an error, and it will be fixed and re-checked.