Calculators · Cement Calculator

Concrete & masonry

Cement Calculator

Enter a slab size or a volume to get the bags of 94 lb portland cement, plus the sand and gravel for a 1:2:3 mix.

Length

Width

Thickness

Sand parts

Cubic feet of sand per bag. Empty uses the SAKRETE 1:2:3 mix.

Gravel parts

Cubic feet of gravel per bag. Empty uses 3.

Concrete per bag (ft³)

Empty uses 4.5, the SAKRETE yield of one 94 lb bag. Change it if your mix is different.

Waste to add (%)

Optional. Empty counts as 0%.

Cement, concrete or mortar? Know what you are buying

In everyday speech “cement” can mean three different things. The bag you pick up depends on which one you mean. This calculator is for the first row, portland cement, which you mix yourself with sand and gravel. If you want a bag that only needs water, you want concrete mix and the concrete calculator is the better fit, although the result above also shows how many 80 and 60 lb bags the same job would take.

What you want	What goes in it	Mix by volume
Portland cement	The binder only, in 94 lb bags of 1 ft³ each	Not applicable
Concrete you mix yourself	Cement, sand, gravel and water	1 cement : 2 sand : 3 gravel
Type S mortar (ASTM C270)	Cement, Type S hydrated lime and masonry sand	1 : ½ : 3½ to 4½
Type N mortar (ASTM C270)	Cement, Type S hydrated lime and masonry sand	1 : 1 : 4¾ to 5¾

The mixes come from the QUIKRETE Portland Cement data sheet (revised August 2022, checked October 2026). For walls built with bricks or blocks, the brick calculator and the concrete block calculator count the mortar for you.

How to calculate how many bags of cement you need

First find the volume of concrete in cubic feet. Then divide it by the volume of concrete that one bag of cement makes. SAKRETE states on its Portland Cement sheet (revision 3-10, checked October 2026) that a 94 lb bag is 1 cubic foot of cement and that, mixed 1:2:3 with about 6 gallons of water, it makes 4.5 cubic feet of concrete.

Step	Formula
1. Cubic feet of concrete	length (ft) × width (ft) × thickness (ft)
2. Add waste, if you want it	cubic feet × (1 + waste ÷ 100)
3. Bags of cement	cubic feet ÷ 4.5, rounded up
4. Sand and gravel	bags × 2 cubic feet of sand and bags × 3 cubic feet of gravel

A cubic yard is 27 cubic feet, so that is 27 ÷ 4.5 = 6 bags per cubic yard. QUIKRETE says that five to six 94 lb bags are typically used per cubic yard of concrete. The calculator shows that range next to its own count, because the real number depends on the mix, the sand and the gravel you use.

Example: a 10 ft by 10 ft slab, 4 inches thick

A small patio is 10 ft by 10 ft and 4 inches thick. You add 10% waste. These are the figures you get on the “Slab or area” tab.

Step	Operation	Result
Thickness in feet	4 ÷ 12	0.3333 ft
Volume	10 × 10 × 0.3333	33.33 ft³
With 10% waste	33.33 × 1.10	36.67 ft³
Cement	36.67 ÷ 4.5 = 8.15, rounded up	9 bags of 94 lb
Sand	8.15 × 2	16.30 ft³ (0.60 yd³)
Gravel	8.15 × 3	24.44 ft³ (0.91 yd³)
Water	8.15 × 6 gallons	about 49 gal
QUIKRETE range	1.358 yd³ × 5 and × 6, rounded up	7 to 9 bags

Bags of cement for common slab sizes

These figures are for a slab 4 inches thick and no waste, with the SAKRETE yield of 4.5 cubic feet per bag.

Slab size	Cubic feet	Cubic yards	94 lb bags (SAKRETE)	94 lb bags (QUIKRETE range)
10 ft × 10 ft	33.33	1.23	8	7 to 8
12 ft × 12 ft	48.00	1.78	11	9 to 11
16 ft × 16 ft	85.33	3.16	19	16 to 19
20 ft × 20 ft	133.33	4.94	30	25 to 30
24 ft × 24 ft	192.00	7.11	43	36 to 43

What goes in the mix with the cement

Sand. SAKRETE lists 2 parts of concrete sand or general purpose sand, 160 to 180 lb per bag of cement. Divided per cubic foot that is 80 to 90 lb, and the calculator uses those figures for the weight line.
Gravel. 3 parts of gravel or stone, 240 to 300 lb per bag of cement, with ¾ inch recommended. That is 80 to 100 lb per cubic foot. To order it by the ton, see the gravel calculator.
Water. About 6 gallons per bag for the 1:2:3 mix, according to SAKRETE. The calculator only shows water when you keep the mix on the sheet’s values.
Thin pours. For anything under 2 inches thick and for toppings, SAKRETE gives a different mix of 1 part cement to 3 or 4 parts sand. This calculator does not size it, so check the sheet.

The weights per cubic foot are a division of SAKRETE’s figures by the number of parts, so treat them as a guide. Moisture and the size of the stone change the real weight.

Prefer bagged concrete mix?

If you only want to add water, buy concrete mix. The result lists the 80 lb and 60 lb bags for your volume with the QUIKRETE yields of 0.60 and 0.45 cubic feet. For slabs, footings, walls and steps with every size of bag, use the concrete calculator. This page does not show prices, because they change by region and supplier. Take the bag counts to a local supplier and ask for a quote.

Frequently asked questions

How many bags of cement do I need for a 12x12 slab?

At 4 inches thick the slab is 48 cubic feet. With the SAKRETE yield of 4.5 cubic feet of 1:2:3 concrete per 94 lb bag, that is 10.67 bags, so buy 11. QUIKRETE says a cubic yard takes 5 to 6 bags, which gives 9 to 11 bags for the same slab. At 6 inches thick the slab is 72 cubic feet, which is 16 bags with SAKRETE and 14 to 16 with QUIKRETE.

How many bags of cement are in a cubic yard of concrete?

SAKRETE says one 94 lb bag makes 4.5 cubic feet of concrete, so a cubic yard of 27 cubic feet takes 6 bags. QUIKRETE says five to six 94 lb bags are typically used per cubic yard. The calculator shows both so you can see the range.

How many cubic feet is a 94 lb bag of cement?

One cubic foot. SAKRETE prints it on its Portland Cement sheet: the 94 lb bag contains 1 cubic foot. That is why one “part” in a mix such as 1:2:3 is one cubic foot per bag of cement.

What is the difference between cement and concrete?

Cement is the binder. Concrete is cement plus sand, gravel and water, as in the 1:2:3 mix on the SAKRETE sheet. Bags labeled “concrete mix” already hold all the dry parts, so you only add water. A bag of portland cement does not, so you also have to buy the sand and the gravel.

What is the 4-2-1 rule for concrete?

SlashGear describes it as four parts gravel, two parts sand and one part cement, also written 1-2-4. The manufacturer sheets used here give 1:2:3 and a yield for it, which is why the calculator starts from 1:2:3. If you mix 1:2:4, type 4 in the gravel box and the concrete that your mix really makes per bag in the yield box.

How much cement do I need for mortar?

This calculator does not size mortar. QUIKRETE gives mortar mixes by volume, such as 1 part cement to one half part lime to 3.5 to 4.5 parts masonry sand for Type S, but neither QUIKRETE nor SAKRETE publishes how much mortar a bag of cement yields. For brick and block walls, use the brick or concrete block calculator, which count mortar for you.

How much sand and gravel go with each bag of cement?

In a 1:2:3 mix each 94 lb bag takes 2 cubic feet of sand and 3 cubic feet of gravel. SAKRETE lists 160 to 180 lb of sand and 240 to 300 lb of gravel for that, with about 6 gallons of water. The calculator multiplies those amounts by the number of bags.

The 4-2-1 definition comes from an informational site, SlashGear, not from a manufacturer.