Cement Calculator
Work out Portland cement bags, sand, gravel, and water for any concrete or mortar mix ratio.
Your Cement Estimate
- Enter your pour size - length and width in feet, thickness in inches - or type a known volume in cubic yards to skip the geometry.
- Pick a mix ratio - 1:2:3 for general slabs and patios, 1:1.5:3 where strength matters, a mortar ratio for masonry work.
- Choose the bag size - 94 lb is the US standard Portland cement bag; 47 lb half bags are easier to carry.
- Set the waste factor - 10% covers hand-mixing spillage and an uneven subgrade; drop to 5% for machine mixing in clean forms.
- Read all four materials - the result gives cement bags plus the sand, gravel, and water that complete the mix - order them together.
One cubic yard of standard 1:2:3 concrete takes about 7 bags of 94 lb Portland cement, 14 cubic feet of sand, and 21 cubic feet of gravel. A leaner 1:2:4 mix drops that to about 6 bags per yard; a stronger 1:1.5:3 mix raises it to about 8. Enter your pour size and ratio above for exact quantities - including the water.
Cement Is Not Concrete - What This Calculator Figures
Cement is the gray binding powder; concrete is what you get after mixing that powder with sand, gravel, and water. This calculator is for people batching their own concrete or mortar from bags of straight Portland cement - it splits your pour volume into all four ingredients by your chosen mix ratio. If you are buying premixed bags instead (Quikrete, Sakrete - the bags that already contain sand and gravel), you want the Concrete Bag Calculator, which counts 40, 60, and 80 lb premix bags directly.
The distinction matters at the register: a 94 lb bag of Portland cement and an 80 lb bag of concrete mix look similar on the shelf but are completely different products. The 94 lb bag is pure binder and makes roughly 6 cubic feet of concrete once you add your own sand and gravel; the 80 lb premix bag makes 0.6 cubic feet and needs only water. Site-mixing from straight cement is usually cheaper per cubic foot on medium jobs, at the cost of handling three materials instead of one.
What a 1:2:3 Mix Ratio Means
Concrete and Mortar Mix Ratios Compared
Nominal volume ratios trade cement (cost) against strength. These are the common US residential mixes and where each belongs - approximate compressive strengths assume proper water content and curing:
| Mix ratio | Approx. strength | Cement per yd³ | Typical use |
|---|---|---|---|
| 1 : 2 : 3 | ~3,000 PSI | 7 bags (94 lb) | Slabs, patios, sidewalks, general work |
| 1 : 2 : 4 | ~2,500 PSI | 6 bags | Economy pours, non-structural fill with form |
| 1 : 1.5 : 3 | ~4,000 PSI | 8 bags | Driveways, footings, loaded slabs |
| 1 : 3 : 6 | Lean mix | 4-5 bags | Blinding layers, haunching, mass fill |
| 1 : 3 (mortar) | Type S-class | 9 bags | Structural masonry, below grade |
| 1 : 4 (mortar) | Type N-class | 7-8 bags | General brick and block laying |
| 1 : 5 (mortar) | Type O-class | 6 bags | Interior, non-load-bearing, repointing |
How the Calculator Works It Out
The dry-volume method, step by step:
Dry loose volume = Wet volume × 1.54 (concrete) or × 1.33 (mortar)
Cement share = Dry volume × cement parts ÷ sum of all parts
Cement weight = Cement share (ft³) × 94 lb/ft³
Bags = Weight × (1 + waste) ÷ bag size, rounded up
Sand / gravel = Dry volume × their parts ÷ sum of parts, plus waste
Water = Cement weight × 0.50 ÷ 8.34 lb per gallon
Why Dry Volume Is 54% More Than the Pour
Loose cement, sand, and gravel are full of air voids. When water is added and the mix is compacted, the fine particles pack into the voids between the coarse ones and the total volume shrinks by roughly a third. Working backwards, you need about 1.54 cubic feet of loose dry material for every cubic foot of finished concrete - that is the 1.54 factor in the formula chain, and skipping it is the classic reason site-mixed batches come up short. Mortar, with no coarse aggregate, compacts less: the factor is about 1.33.
The water figure the calculator returns assumes a water-to-cement ratio of 0.50 by weight - around 5 to 6 gallons per 94 lb bag. That is a sound general-purpose number: enough for full hydration and workability without badly diluting strength. Lower ratios (0.40-0.45) give stronger, less permeable concrete but get stiff to place; anything above 0.60 costs real strength. Add water gradually - aggregate moisture varies, and it is far easier to add a quart than to rescue a soup.
Sources & Standards
- Bag weight and the one-bag-equals-one-cubic-foot convention follow the US standard for Portland cement: a bag is 94 lb, corresponding to a bulk density of 94 lb/ft³. All cement types sold in the US (Type I/II is the bag-store default) are governed by this specification.ASTM C150 - Standard Specification for Portland Cement
- Nominal volume ratios are a field-batching convenience. Engineered work is proportioned by weight and water-cement ratio instead - the ACI method targets a specified strength and slump rather than fixed parts. Use this calculator for estimating and DIY batching, and follow the project mix design where one exists.ACI 211.1 - Standard Practice for Selecting Proportions for Normal Concrete
Worked Example: 12 × 10 ft Patio, 4 Inches Thick
Wet volume: 12 × 10 × (4 ÷ 12) = 40 cubic feet, or 1.48 cubic yards. Dry loose volume at the 1.54 factor: 61.6 cubic feet. With the standard 1:2:3 ratio the parts sum to 6, so cement takes 61.6 ÷ 6 = 10.3 cubic feet. At 94 lb per cubic foot that is 965 lb; add 10% waste for 1,062 lb, which rounds up to 12 bags of 94 lb Portland cement.
The same split gives about 23 cubic feet of sand (0.84 yd³) and 34 cubic feet of gravel (1.25 yd³) including waste, plus roughly 64 gallons of mixing water at w/c 0.50. Order the sand and gravel by the cubic yard - the Sand Calculator converts that to tons for the supplier.
Frequently Asked Questions
How many bags of cement do I need for 1 yard of concrete?
What is the difference between cement and concrete?
Should I buy Portland cement or premixed concrete bags?
What mix ratio should I use for a driveway?
How much water do I add per bag of cement?
Can I use a mortar ratio like 1:4 for a slab?
After You Know Your Bag Count
Cement is one of four ingredients. Here is the usual sequence from here:
Batching your own to save money? Benchmark against what a finished concrete slab actually costs in 2026 - materials and labor, by size and region.