Cement Calculator
Mixing concrete or mortar from scratch? Enter the volume and your mix ratio to find out how many bags of cement you need, plus the sand and gravel quantities.
Understanding Cement in Concrete
Cement is the glue that holds concrete together. When mixed with water, it forms a paste that coats sand and gravel particles. As the paste cures, it hardens into a solid matrix that binds everything into a strong, durable mass.
Portland cement is the most common type. It comes in different formulations (Type I, II, III, etc.) for various applications. Type I is standard for most residential work. Type II resists sulfates in soil. Type III gains strength quickly for cold-weather pours.
The amount of cement in a mix determines strength and cost. More cement means stronger concrete but higher expense. The trick is using just enough cement to meet your strength requirements without overspending on material.
Mix Ratios Explained
Mix ratios express the proportions of cement, sand, and gravel by volume. A 1:2:3 ratio means 1 part cement, 2 parts sand, and 3 parts gravel. This is a common all-purpose mix that produces concrete around 3000 psi.
Richer mixes use more cement. A 1:1.5:2.5 ratio increases the cement content, raising strength to 4000 psi or more. These mixes cost more but handle heavy loads and harsh conditions better.
Mortar mixes omit the gravel. A typical mortar ratio is 1:3 or 1:4 (cement to sand). Mortar is used for laying brick, block, and stone, where a finer texture is needed to bond masonry units.
Calculating Cement Quantities
Start with the total volume of concrete you need in cubic yards or cubic feet. Divide that volume by the sum of the mix ratio parts to find the volume of cement. For example, a 1:2:3 mix has 6 total parts, so cement is 1/6 of the total volume.
Convert cement volume to bags. One 94-lb bag of cement equals roughly 1 cubic foot. If you need 5 cubic feet of cement, buy 5 bags. Always round up and add a bag or two for waste and spillage.
Sand and gravel volumes follow the same logic. Multiply the cement volume by the respective ratio numbers. For a 1:2:3 mix, sand is twice the cement volume and gravel is three times the cement volume. Measure aggregates by volume, not weight, for consistency.
Frequently Asked Questions
What is the difference between cement and concrete?
Cement is the powder that binds aggregate together. Concrete is cement mixed with sand, gravel, and water. Cement is an ingredient; concrete is the finished product.
How much does a bag of cement weigh?
A standard bag of Portland cement weighs 94 pounds in the US. It yields approximately 1 cubic foot of dry cement.
What is a common concrete mix ratio?
A 1:2:3 ratio (1 part cement, 2 parts sand, 3 parts gravel by volume) is common for general-purpose concrete. This produces roughly 3000 psi strength.
Can I use cement without sand and gravel?
Pure cement paste is weak and prone to cracking. Sand and gravel add strength, reduce shrinkage, and lower cost. Always use a proper mix for structural work.
How do I store cement bags?
Keep bags dry and off the ground. Stack on pallets and cover with plastic. Cement exposed to moisture hardens in the bag and becomes unusable.