Dry Pour Concrete Calculator
Use this dry pour concrete calculator to estimate how much bagged concrete you need for a dry-pour slab. Enter the slab dimensions, choose your wastage allowance, and the tool will estimate the required volume and the number of bags based on the selected bag size. It can also estimate cost if you enter a price per bag.
How this calculator works
This calculator works out the slab volume by multiplying length, width, and thickness using consistent units. It then applies the wastage allowance entered by the user and converts the result into the volume units shown by the calculator. Using the selected bag yield, it estimates how many bags are needed and rounds up so you have a whole number of bags for planning and purchasing.
Formulas used
volume = length × width × thickness
adjusted volume = volume × (1 + waste % / 100)
bags needed = ⌈adjusted volume / yield per bag⌉
estimated cost = bags needed × price per bag
cubic feet = cubic metres × 35.3147
Dry-pour projects still rely on the same volume maths as any other slab estimate. Final bag counts depend on the actual yield of the product being used.
Worked example
Take a slab measuring 3 m by 2 m at 100 mm thick. That gives a base volume of 0.6 m³ before any wastage allowance is added. If the user adds a waste percentage, the required volume rises accordingly, and the calculator then divides that adjusted volume by the yield of the chosen bag size to estimate the number of bags required.
About dry pour concrete
Dry pour concrete uses the same basic volume calculation as any other slab estimate, but the project method differs because the material is placed and hydrated in position rather than fully mixed first. This calculator helps with the quantity side only. It does not decide whether dry pouring is suitable for your slab design, ground conditions, or intended structural use.
Frequently asked questions
Related tools
- Concrete Slab Bag Calculator — how many bags of concrete for a slab
- Concrete Volume Calculator — calculate concrete volume for slabs, footings, and columns
- Concrete Truck Load Calculator — estimate ready-mix delivery loads
- Weight of Concrete Slab Calculator — estimate the total weight of a concrete slab
Guides worth reading
- Does Dry Pour Concrete Work? An Honest UK Guide — where it's fine, where it fails BS 8500 strength, and a worked shed-base example
Disclaimer: This calculator is for planning and estimating only. Actual bag counts and costs can vary with product yield, waste, and site conditions. Always check the product information and installation guidance before ordering or pouring.