Cement Calculator
Estimate cement quantity in bags, cubic yards, and cubic feet for slabs, footings, and repairs.
Your Cement Estimate
- Measure your area — length and width in feet or meters.
- Set thickness — 4 inches for standard slabs, 6 inches for driveways. Use presets or enter custom values.
- Choose waste factor — 10% is recommended for most jobs.
- Review results — compare cubic yards, bag counts, and decide between bags and ready-mix.
- Order materials — round up bag counts and confirm pricing with your supplier.
Cement vs. Concrete — What's the Difference?
Cement and concrete are often used interchangeably, but they're different materials. Cement (Portland cement) is a fine powder that acts as the binding agent. Concrete is the finished product made by mixing cement with water, sand, and aggregate (gravel or crushed stone). When you buy a bag of "concrete mix" at the hardware store, it already contains cement, sand, and aggregate in the right proportions — just add water.
This calculator estimates the total volume of concrete you need (which includes cement as an ingredient). If you're mixing from scratch instead of using pre-mixed bags, a standard ratio is 1 part cement to 2 parts sand to 3 parts gravel by volume, with roughly 0.5 parts water.
Concrete Mix Ratios by Strength
| Mix Type | Cement | Sand | Gravel | Approx. Strength |
|---|---|---|---|---|
| Standard (1:2:3) | 1 part | 2 parts | 3 parts | 3,000–3,500 PSI |
| Rich mix (1:1.5:3) | 1 part | 1.5 parts | 3 parts | 4,000–4,500 PSI |
| Lean mix (1:3:6) | 1 part | 3 parts | 6 parts | 2,000–2,500 PSI |
| High strength (1:1:2) | 1 part | 1 part | 2 parts | 5,000+ PSI |
Water-to-cement ratio of 0.45–0.55 for most mixes. Less water = stronger concrete, but harder to work.
Pre-Mixed Bag Coverage
Pre-mixed bags are the simplest option for small projects. Here's what each size yields:
| Bag Weight | Volume Yield | Bags per Cubic Yard | Best For |
|---|---|---|---|
| 80 lb (36 kg) | 0.60 ft³ | 45 bags | Most projects — best value per bag |
| 60 lb (27 kg) | 0.45 ft³ | 60 bags | Easier to carry — good for solo work |
| 50 lb (23 kg) | 0.375 ft³ | 72 bags | Quick-setting mixes, post holes |
| 40 lb (18 kg) | 0.30 ft³ | 90 bags | Small repairs, patching |
Tip: 80 lb bags offer the best cost per cubic foot, but 60 lb bags are much easier on your back. For large projects, the labor difference adds up.
How the Calculator Works
Simple volume math converts your project dimensions to concrete quantity:
Cubic Yards = Volume ÷ 27
Bags (80 lb) = Volume ÷ 0.60, rounded up
Adjusted = All results × (1 + Waste %)
The waste factor accounts for uneven subgrade, spillage, and material left in the mixer. 10% is standard for most residential work.
Related Calculators
Cement is just one part of the mix — add aggregate and water. See the full construction calculator collection.
Common Questions
How many bags of cement do I need for a 10×10 slab?
At 4 inches thick, a 10×10 ft slab needs approximately 1.23 cubic yards — that's about 56 bags of 80 lb pre-mixed concrete. This is for complete concrete mix (cement + sand + gravel), not pure cement powder alone.
What is the difference between cement and concrete?
Cement is an ingredient — concrete is the finished product. Concrete is made from cement (Portland cement), sand, aggregate (gravel), and water. Cement alone has no structural value; it is the binder that holds concrete together. When people say "cement driveway" they almost always mean concrete.
Does cement go bad?
Yes. Cement absorbs moisture from air and begins to hydrate slowly. Unopened bags stored off the ground in a dry environment last 3–6 months. Bags that feel hard or lumpy have partially hydrated and will produce weaker concrete. Never use cement with hardened lumps for structural work.
Can I mix Portland cement with sand and gravel myself?
Yes. A standard site-mixed concrete uses approximately 1 part Portland cement, 2 parts sand, and 3 parts gravel by volume, plus water. A stiffer mix (less water) produces stronger concrete. For structural work, keep the water-to-cement ratio at 0.45 or lower. Bagged pre-mixed concrete (Quikrete, Sakrete) is easier for small jobs since proportions are already dialed in.
What is the difference between Type I, Type II, and Type III Portland cement?
Type I (general purpose) is standard for most residential slabs, footings, and walls. Type II resists moderate sulfate exposure and generates less heat — common in larger pours and sulfate-bearing soils. Type III gains strength faster, useful in cold weather or when formwork needs to come off quickly. Most bagged concrete (Quikrete, Sakrete) uses Type I/II blended.