Concrete Calculator
Estimate concrete for slabs, rectangular strips and round forms. Compare whole bags using product-specific yield with a rounded ready-mix volume.
Measure the form. Check the yield.
View the formulas ↗Enter measured dimensions
Use length, width and thickness for slabs or diameter and depth for round forms. Repeat identical forms with a count.
Use the actual mix yield
Select a documented product example or enter the yield from the bag. Equal bag weights can have different yields.
Allow and round separately
Apply a chosen allowance, then round bags or ready-mix increments upward. See both effects in the breakdown.
Small details. Better estimates.
Explore all 6 guides ↗Concrete slab volume: from measured dimensions to bags or yards
Calculate a slab quantity, apply a separate allowance, and convert it to named-product bags without choosing structural dimensions.
Read the guide ↗Guide 02 / Worked examplesConcrete for round tubes and post holes
Calculate cylinder volume, repeat identical pours, and subtract only a post that actually occupies the concrete space.
Read the guide ↗Guide 03 / Worked examplesEstimating strip concrete volume without double-counting corners
Calculate rectangular strips and continuous rings from supplied design dimensions, with an explicit corner example.
Read the guide ↗Guide 04 / Worked examplesConcrete bag yield: why bag weight alone is not enough
Compare manufacturer-stated yields, calculate whole bags, and avoid confusing dry weight with finished volume.
Read the guide ↗Guide 05 / Worked examplesConcrete allowances and ready-mix order rounding
See how measurement changes, allowances and supplier increments affect an order without treating any percentage as a guarantee.
Read the guide ↗Guide 06 / Worked examplesConcrete in cubic metres, litres and cubic yards
Calculate metric pours directly and convert volumes without confusing kilograms with litres or mixing thickness units.
Read the guide ↗Before you calculate
Does an 80 lb bag always yield 0.6 ft³?
No. QUIKRETE Concrete Mix No. 1101 lists approximately 0.60 ft³ for its 80 lb bag; SAKRETE PRO-X180 lists about 0.59 ft³ for its 80 lb bag. Check your exact product.
What thickness should my slab be?
This tool calculates the dimensions you enter. It does not select structural thickness, reinforcement, load capacity or footing dimensions. Use project specifications and qualified local advice.
Is the allowance required?
The percentage is your planning assumption. Actual over-excavation, forms, losses and supplier requirements vary. The calculator separates allowance from package rounding.
How do I avoid counting corners twice?
For intersecting strips, split the plan into non-overlapping rectangles or subtract each overlap once. The guide includes a worked example.