Concrete Calculator
Fill in only the parts you need — empty items count as zero
Concrete Calculator: Estimate Concrete, Cement, Sand & Aggregate Cost
This free concrete calculator estimates how much concrete, cement, sand and aggregate you need for a project, and what the materials will cost. It covers slabs, square footings and walls, post holes, rectangular and round columns, circular slabs, pipe fill, curbs and gutters, and stairs with landings, using the mix ratio for M15, M20 or M25 concrete.
Quick answer: concrete volume for a slab is length × width × thickness, plus 5 to 10 percent for waste. A 5 m × 4 m slab that is 150 mm thick needs 3 m³, about 3.15 m³ with 5 percent waste, which is roughly 26 bags of cement in an M20 mix.
How Concrete Volume Is Calculated
Rectangular slabs, footings and walls use length × width × thickness (or height). Round columns and circular slabs use the cylinder formula. The calculator then converts the wet volume into dry materials by multiplying by 1.54, which accounts for voids and shrinkage when the mix is compacted.
Concrete Mix Grades: M15, M20 and M25
The grade sets how much of the dry volume is cement, sand and aggregate. A stronger grade uses more cement per cubic meter, so it costs more.
| Grade | Mix ratio (cement : sand : aggregate) | Cement bags per m³ | Typical use |
|---|---|---|---|
| M15 | 1 : 2 : 4 | about 6.3 | Paths, simple flooring and light work |
| M20 | 1 : 1.5 : 3 | about 8.1 | Residential slabs, foundations and footings |
| M25 | 1 : 1 : 2 | about 11.1 | Heavy structural and reinforced concrete |
Cement, Sand and Aggregate Quantities
Your dry volume is split by the mix ratio. For M20 the parts are 1 + 1.5 + 3 = 5.5, so cement is 1/5.5 of the dry volume, sand 1.5/5.5 and aggregate 3/5.5. Cement is converted into bags using 0.0347 m³ for each 50 kg bag. Enter your local prices for cement, sand and aggregate and the calculator totals the material cost, with a waste slider for spillage and over-excavation.
Estimating Slabs, Columns, Stairs and Curbs
Slabs and footings — length × width × thickness, multiplied by the quantity.
Columns and post holes — rectangular or round, multiplied by the quantity.
Pipe fill — the ring between the outer and inner diameter, times the height.
Curb and gutter — length × the average of the bottom and top width × height.
Stairs — solid steps built up from the ground, plus any landing.
Fill in only the parts you need. Items left empty count as zero, so the totals always match your project. To find the area of an irregular slab first, use the area calculator.
Tips for Ordering Concrete
Order 5 to 10 percent extra, check the depth of the base in several places and measure after any excavation. The calculator works in cubic meters. To convert to cubic yards, multiply by 1.308, or use the volume converter. It estimates materials only, not labor, reinforcement or formwork. Prices vary by region, so enter local rates, and for structural work such as beams, columns or foundations ask a qualified engineer and check local building codes.
Who Uses a Concrete Calculator?
Civil engineers, contractors, builders, architects, masons, quantity surveyors, developers, renovation professionals, construction students and DIY homeowners all use it to cut waste, plan budgets and avoid shortages that stop a pour halfway.
How to Use This Concrete Calculator
Choose a concrete grade
Pick M15, M20 or M25 for your type of work.
Enter material prices
Add the cost of cement per bag, and sand and aggregate per cubic meter.
Add your dimensions
Fill in length, width, thickness, height, diameter or quantity for each part of the job.
Set the waste factor
Use the slider. 5 to 10 percent is typical.
Read your results
See total volume, cement bags, sand, aggregate and the total material cost.