Site-Mix Materials Estimator
Estimate the cement, sharp sand and coarse aggregate to mix concrete yourself. Enter the finished volume you need, choose a volume ratio, and adjust the starting assumptions to match your materials.
Results
Enter your project measurements to see your results.
What site-mixed concrete is
Site-mixed concrete is batched where it is used, in a mixer or by hand, from cement, sand, coarse aggregate and water. It suits small or awkward jobs. For larger pours, the ready-mix calculator helps you order delivered concrete, and the concrete bag calculator covers pre-blended bags. Work out a volume first with the concrete calculator or the concrete slab calculator.
Cement, sharp sand and coarse aggregate
Cement is the binder that reacts with water. Sharp sand is a coarse, angular fine aggregate that fills spaces between stones — not soft building sand used for mortar. Coarse aggregate is gravel or crushed stone, commonly up to 10 or 20 mm. Some suppliers sell a pre-blended “all-in” ballast instead of separate sand and stone.
How volumetric ratios and the dry-volume factor work
A ratio such as 1:2:4 means one bucket of cement to two of sand and four of aggregate. Loose dry materials do not add up to the same volume of concrete: finer particles fill voids and the mix compacts. The calculator multiplies the finished volume by a dry-volume factor, then divides the result by the total parts. The factor is an estimate; aggregate grading, moisture (which bulks sand), compaction and mixing practice all change the real yield.
Water and strength
Water quantity and water/cement ratio must follow your mix design or product guidance; this page does not calculate them. Nominal ratios do not establish a certified strength. Footings, slabs carrying loads and anything structural need a suitable specified concrete mix — see guidance from bodies such as the Concrete Centre, the Portland Cement Association or your building control authority.
Worked metric example
A 4 m × 2.5 m pad at 100 mm is 1.0 m³, or 1.1 m³ with 10% waste. With the starting assumptions (1:2:4, factor 1.54) the dry volume is 1.694 m³: cement 0.242 m³ ≈ 348 kg (14 × 25 kg bags), sharp sand 0.484 m³ ≈ 774 kg and aggregate 0.968 m³ ≈ 1,452 kg.
Worked imperial example
A 10 ft × 10 ft area at 4 in is about 1.23 yd³. With 10% waste and the same assumptions, that needs roughly 730 lb of cement (8 × 94 lb bags), 1,610 lb of sand and 3,030 lb of aggregate.
Limitations
This tool provides materials estimates only. It is not certified concrete strength or structural design advice, and actual quantities depend on your materials and methods. Related: mortar calculator, floor screed calculator.
Frequently asked questions
- How much cement, sand and aggregate do I need for 1 m³ of concrete?
- Using this page's editable starting assumptions (1:2:4 by volume, 1.54 dry-volume factor, 1,440 kg/m³ cement, 1,600 kg/m³ sand, 1,500 kg/m³ aggregate), 1 m³ needs roughly 317 kg of cement, 704 kg of sharp sand and 1,320 kg of coarse aggregate before waste. Your materials and mixing will change the real figures.
- Does a 1:2:4 mix give a particular concrete strength?
- No. A nominal volume ratio describes proportions, not a certified strength. Strength depends on the cement, aggregate grading, water content, mixing, compaction and curing. Structural work needs a specified mix, usually from a designer or ready-mix supplier.
- Why multiply by a dry-volume factor?
- Loose dry materials contain air gaps. When sand fills the spaces between stones and cement fills the spaces in the sand, the combined volume shrinks. The factor — 1.54 here as an editable starting estimate — accounts for that, but it is not a fixed value.
- How much water should I add?
- This calculator does not estimate water. Follow your mix design or the cement manufacturer's guidance. Adding extra water makes mixing easier but reduces strength and durability.
- Are all bulk bags the same weight?
- No. Suppliers sell bulk bags of different weights, and the volume of a bag varies with the material. Enter the weight stated by your supplier to get a rounded count.