Cement Calculator: How Many Bags of Cement Do You Need?

For a 1:2:3 mix, plan on about 7 bags of 94-lb Portland cement per cubic yard before waste. With 10% waste, most projects round up to 8 bags. Richer mixes need more cement: 1:1.5:3 is about 8 bags per yard and 1:1:2 is about 10 bags per yard.

For a 1:2:3 mix, one cubic yard needs about 8 bags of 80-lb Portland cement before waste. An 80-lb bag contains about 0.85 ft3 of cement, compared with 1.00 ft3 in a 94-lb bag.

Portland cement is pure cement that must be mixed with sand, gravel, and water. Concrete mix bags already contain cement, sand, and gravel. This calculator is for Portland cement only; use the concrete bag calculator for pre-mixed concrete bags.

Using the correct volume formula, a 20 x 20 ft patio at 4 inches thick is 4.94 yd3. For a 1:2:3 mix with 10% waste, that is about 37 bags of 94-lb Portland cement, plus sand, gravel, and water.

For a standard 1:2:3 mix at w/c = 0.50, use about 5.5 gallons of water per 94-lb bag of Portland cement. Add water gradually and avoid making the mix soupy.

Opened Portland cement should be used within 24-48 hours in humid conditions, or within 2-4 weeks if sealed in a heavy-duty plastic bag with air removed. Hard lumps that do not crumble mean the cement has pre-hydrated and should be discarded.

For very small jobs, bags are usually cheaper. Around 1.0-2.5 yd3, cost is often close. Above that, ready-mix usually wins when labor, quality, and continuous pour timing are considered.