Concrete and cement bag calculator
Estimate wet concrete volume, cement bags, sand, and gravel for a slab or round columns.
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Tool guide
Concrete and cement bag calculator: how it works
Practical information to understand the result and use this tool correctly.
About Concrete and cement bag calculator
This calculator turns a slab or a set of round columns into wet cubic meters, then into a buying list: cement bags, sand, and gravel.
Dry volume is the wet volume multiplied by 1.54, a common allowance for voids in sand and aggregate. Cement, sand, and gravel are split by the mix parts you pick. A 50 kg bag is treated as about 0.035 m³ of cement (bulk density 1,440 kg/m³).
Use it to order materials for a patio, sidewalk, or post bases. It is a planning estimate, not a structural design. Local mixes, bag weights, and waste vary.
Nothing is uploaded. Change the waste percentage if the pour is uneven or you expect spillage.
How to use it
- 1Choose a slab or round columns, then apply a preset or type the dimensions and thickness.
- 2Pick a mix (1:3:5, 1:2:3, or 1:1.5:3) and a bag size. Add waste if you need spare material.
- 3Read wet volume, bags to buy, sand, gravel, and an optional bag-price total.
- 4Copy the result before ordering. Round bags up; suppliers sell whole bags.
Frequently asked questions
- How is the concrete volume calculated?
- For a slab, wet m³ = length × width × thickness. For columns, wet m³ = count × π × radius² × height. Waste is applied after that.
- How many cement bags are in one cubic meter?
- It depends on the mix. With 1:2:3 and the 1.54 dry factor, one wet cubic meter is about 7 bags of 50 kg. A leaner 1:3:5 mix uses fewer bags.
- Which bag size should I select?
- Match the bag sold locally: 25 kg, 40 kg, 42.5 kg, or 50 kg. The cement mass stays the same; only the bag count changes.
- Is this a structural specification?
- No. It estimates materials for a small pour. Footings, slabs on grade, and reinforced concrete need a local spec or an engineer.
- Are the dimensions uploaded?
- No. The calculation runs in the browser.