Concrete calculator
Concrete Slab Materials Calculator
Enter the slab and specified base dimensions to get one quantity list. Add a rebar grid only when its spacing, bar size, and inset are already specified for your project.
Planning estimate, not a contractor quote. Review the assumptions and replace presets with local prices when available.
Method
How this calculator works
A slab project requires separate material quantities. This worksheet combines the concrete-volume calculation with aggregate-base volume and an optional rectangular rebar takeoff. Concrete and base have separate allowances. Steel uses a separate cut and splice allowance. No structural dimensions are selected by this tool.
Concrete = length × width × thickness × concrete allowance. Base = length × width × base depth × base allowance. Base tons = adjusted cubic feet × density ÷ 2,000. Steel = the sum of drawing-specified grid runs plus the entered steel allowance.
Worked example
A realistic starting point
A 10 × 10 ft slab, 4 in thick, with 10% concrete allowance needs a 1.50 yd³ order or 62 nominal 80 lb bags. A separate 4 in base at 105 lb/ft³ with 10% allowance contains about 1.36 yd³ and rounds to a 2 US ton order. Rebar is excluded until you enable it and enter the drawing values.
What changes the answer
Factors worth checking
Separate layers
Slab thickness is the concrete layer only. Base depth is the compacted aggregate layer underneath it.
Specified reinforcement
Use bar size, spacing, inset, and layer count from the project design. The optional grid represents one rectangular layer.
Ordering and offcuts
Whole bags, bulk-load rounding, and theoretical stock-bar equivalents use different purchasing conventions.
Other materials
Forms, chairs, tie wire, vapor barriers, drainage, curing products, and specialty details need separate takeoffs.
Common questions
Slab shopping list FAQ
Does this design the slab or reinforcement?
No. It calculates quantities from dimensions and grid settings you supply. It does not determine loads, thickness, bar size, cover, or structural suitability.
Should I order both ready-mix and bags?
Usually these are alternative ways of buying the calculated concrete. The worksheet shows both so you can choose a supply method.
Is this a complete construction shopping list?
It covers concrete, base aggregate, and optionally grid steel. Forms, supports, membranes, drainage, curing materials, and other specification details remain separate.
Evidence
Sources & review
- QUIKRETE Concrete CalculatorManufacturer quantity and whole-bag rounding reference; package data governs yield.
- NRMCA — Concrete in PracticeReady-mix practice and project planning context. Not a source for the example prices.
- FHWA Gravel Roads ManualAggregate and compaction context; supplier product data should determine density.
Published by Calcstead. Report a correction.
Method and source links reviewed September 5, 2026. Price presets are editable planning inputs and should be replaced with current local information.