Cement Calculator

1. Enter the concrete volume and its unit. Size it with the concrete calculator first if you only have dimensions.
2. Pick the mix ratio, or choose Custom parts. The cement count depends on cement being the first number in the ratio.
3. Adjust the dry-volume factor and waste if needed, then read the bags.
4. Buy whole bags: the result is rounded up, with the exact figure in the working line.

Here is what each result means:

A cement calculator works out how many bags of Portland cement a concrete mix needs for a given volume. It is the cement-only answer behind the wider question of how much concrete to buy.

It matters because cement is sold two very different ways, and they are easy to confuse. Portland cement is the grey powder, sold in 94 pound US bags (about one cubic foot) or 50 kilogram bags, that you mix with sand and gravel. Premixed concrete bags, such as an 80 pound bag, already contain the sand and gravel, so they are not the same thing. This tool counts Portland cement powder for a mix ratio; use the concrete calculator for premixed bags.

Dry ingredients take more space than finished concrete, so the wet volume is first multiplied by a dry-volume factor, commonly 1.54. The cement is then its share of that dry volume, set by the first number in the mix ratio.

1. Multiply the wet volume (plus waste) by the dry-volume factor to get the dry material volume in cubic feet.
2. Take the cement share: cement parts divided by the sum of all parts (for 1:2:4 that is one seventh).
3. Count 94 pound bags at one cubic foot per bag, and the same cement as weight and 50 kilogram bags.

Suppose you are mixing 1 cubic yard of concrete at a 1:2:4 ratio, with a 1.54 dry factor.

Calculation: one cubic yard is 27 cubic feet, so the dry volume is 27 x 1.54 = 41.58 cu ft. The cement share is one seventh, so cement is 41.58 / 7 = 5.94 cu ft. At one cubic foot per 94 pound bag that is 6 bags, about 253 kg, or 6 bags of 50 kg.

These are bags of Portland cement powder. You still need roughly two parts sand and four parts gravel to go with them.

The Mix Ratio

A richer mix (more cement, such as 1:1.5:3) needs more bags; a lean 1:3:6 needs fewer. The first number in the ratio is the single biggest driver of the cement count.

The Dry-volume Factor

Most estimates use 1.54. A higher factor raises the cement count, so leave it at 1.54 unless you have a reason to change it.

Bag Size and Standard

A 94 pound US bag is about one cubic foot; a 50 kilogram bag is a little smaller by weight. The tool shows both so you can buy whichever your merchant stocks.

Bulking and Waste

Cement settles and some is lost to the mixer and bags. A waste allowance covers spillage and over-ordering; add more for a long barrow run or a rough site.

The most common mistake is buying the wrong product. Portland cement and premixed concrete are sold in similar-looking bags but do completely different jobs.

This calculator counts Portland cement for a mix you batch yourself. For premixed bags you just add water to, size the job with the concrete calculator instead.

Buying Cement for Site Mixing

Count the bags of Portland cement before you mix your own concrete or mortar.

Splitting a Materials Order

Separate the cement from the sand and gravel on a merchant list so each is ordered in the right quantity.

Checking a Quote

Sanity-check how many bags a supplier has listed against the volume and ratio of your job.

1. Buying Premixed Concrete Instead of Cement

An 80 lb premix bag already has aggregate. If you add your own sand and gravel on top, the mix is wrong. Match the product to the job.

2. Forgetting the Dry-volume Factor

Taking the cement share of the wet volume under-counts bags by about a third. Multiply by the dry factor first.

3. Mixing Up Bag Standards

A 94 lb bag and a 50 kg bag are not the same weight. Order by the figure that matches the bags your merchant sells.

4. Rounding Bags Down

Always round up to whole bags. A part bag still has to be bought, and being one short stops the mix.

5. Treating Nominal Mixes as Structural

The ratios here are nominal. Reinforced or load-bearing work needs a designed mix and cement quantity from an engineer.

The arithmetic is exact for the ratio and factor you enter; real quantities vary with the cement and how it is measured.

For a 1:2:4 nominal mix, about 6 bags of 94 lb Portland cement, or 6 bags of 50 kg. The exact cement volume is one cubic yard x 1.54, then one seventh, which is about 5.94 cubic feet, and one 94 lb bag is about one cubic foot.

No. Portland cement is just the powder you mix with sand and gravel. A premixed concrete bag, such as an 80 lb bag, already contains sand and gravel and only needs water. This calculator counts Portland cement for a mix you batch yourself.

About one cubic foot. Portland cement has a loose bulk density near 94 pounds per cubic foot, which is why a 94 lb bag is packaged as roughly one cubic foot. A 50 kg bag is a little smaller by weight.

A standard US bag is 94 pounds, which is about 42.6 kilograms. The common metric bag is 50 kilograms. The calculator shows both bag counts and the total weight so you can order either.

Take the cement share of the dry volume. For 1:2:4 the parts add to seven, so cement is one seventh of the dry volume. The dry volume is the wet concrete volume multiplied by about 1.54.

No. It counts only Portland cement. For the sand, gravel and water in the same mix, use the concrete mix calculator; for a premixed bag that needs only water, use the concrete calculator.

Most differences come from the bulk-density convention. US estimates use 94 pounds per cubic foot (one bag per cubic foot), while some metric tools use 1440 kilograms per cubic meter, which is a few percent lower. Both are standard.

Treat it as a concrete-mix tool. Mortar and render use cement and sand without gravel and different ratios, so the cement share here will not match a mortar mix. Use a mortar-specific ratio if you adapt it.

Yes. Round up to whole bags and keep a spare, because running short mid-mix stops the pour and a part bag still has to be bought. Store spare cement dry, as it absorbs moisture.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• American Cement Association (Portland Cement Association) (American Cement Association; what Portland cement is).
• National Ready Mixed Concrete Association (NRMCA; concrete materials and proportioning).
• QUIKRETE Concrete Mix product data (QUIKRETE; premixed bag sizes and coverage).
• QUIKRETE concrete and bag calculator (QUIKRETE; bag-count method).