Bags of Cement Per Yard: How Many You Need

This calculator tells you how many bags of cement (portland cement) you need for one cubic yard of concrete, based on the mix ratio you choose. You enter the mix ratio (cement : sand : gravel by volume) and the bag size (typically 94 lb or 42.6 kg), and it returns the number of bags required, plus the volumes of sand and gravel. The standard 1:2:4 mix (1 part cement, 2 parts sand, 4 parts gravel) is the most common for general construction and yields about a 3000 psi concrete.

Formula

The number of bags of cement per cubic yard of concrete is calculated by dividing the total volume of concrete (1 cubic yard = 27 cubic feet) by the sum of the parts in the mix ratio, then multiplying by the cement part (which is 1 for all standard ratios). Then adjust for bag size: a standard 94-lb bag of portland cement equals exactly 1 cubic foot of loose cement. So the formula is:

Bags per yard = (27 / (cement + sand + gravel parts)) × (cement part) × (94 / bag weight in lb)

Where:

• 27 = cubic feet in one cubic yard
• cement, sand, gravel = the parts in your mix ratio (e.g., 1, 2, 4)
• bag weight = weight of one bag of cement in pounds (94 lb is standard in the US, 42.6 kg = 94 lb in metric countries)

Worked Example

Using the default values: mix ratio 1:2:4 and a 94-lb bag.

1. Sum of parts = 1 + 2 + 4 = 7
2. Volume of cement per yard = 27 / 7 = 3.857 cubic feet
3. Since each 94-lb bag is 1 cu ft, bags = 3.857 / 1 = 3.857 bags
4. Rounded to 1 decimal: 3.9 bags

So for a 1:2:4 mix with 94-lb bags, you need about 3.9 bags of cement per cubic yard. In practice, you’d round up to 4 bags.

Why the Mix Ratio Matters

The mix ratio determines the strength and workability of the concrete. The numbers represent the volume proportions of cement, fine aggregate (sand), and coarse aggregate (gravel). Common ratios:

• 1:2:4 – general purpose, ~3000 psi (used for footings, slabs, columns)
• 1:1.5:3 – stronger, ~4000 psi (structural beams, heavy-duty slabs)
• 1:3:6 – lean mix, ~2000 psi (mass concrete, foundations, not for structural)

The more cement you use relative to aggregates, the stronger (but also more expensive and prone to cracking) the concrete. The ratio also affects workability – a richer mix is stickier and harder to place.

How to Read the Result

The calculator gives you the number of bags of cement, but you also need the sand and gravel volumes. For a 1:2:4 mix, the sand volume is (27/7)×2 = 7.7 cu ft and gravel is (27/7)×4 = 15.4 cu ft. These are loose volumes; when mixed with water, the concrete shrinks slightly, so you might need a bit more. Always order 5–10% extra to account for waste, spillage, and uneven subgrades.

Common Mistakes

• Using weight instead of volume for aggregates: Sand and gravel are sold by the cubic yard or ton, not by the bag. A cubic yard of sand weighs about 2,700 lb, gravel about 2,700 lb. If you buy by weight, convert using these densities.
• Forgetting that a 94-lb bag is 1 cu ft: Some bags are 80 lb (0.85 cu ft) or 60 lb (0.64 cu ft). If you use a different size, adjust the bag weight in the calculator.
• Rounding too early: If you round 3.857 to 4 before calculating sand/gravel, you’ll overestimate. Keep decimals until the end.
• Ignoring water: Water is not in the ratio but is essential. Typical water-cement ratio is 0.45–0.60 by weight. Too much water weakens the concrete.

Cost and Buying Considerations

Cement is usually sold in 94-lb bags (1 cu ft) in the US. A typical 1:2:4 mix requires about 4 bags per yard. For a small project like a 10×10 ft slab 4 inches thick (1.23 cubic yards), you’d need about 5 bags of cement, 9.5 cu ft of sand, and 19 cu ft of gravel. Buying pre-mixed concrete from a ready-mix truck is cheaper for large volumes, but for less than 1 yard, bagged concrete (like Quikrete) is more practical – though that’s a different product (already mixed with aggregates).

Alternatives to Mixing Your Own

If you don’t want to mix from scratch, you have options:

• Bagged concrete mix: Contains cement, sand, and gravel already blended. Just add water. A 60-lb bag yields about 0.45 cu ft of concrete, so you’d need about 60 bags per yard (27 / 0.45).
• Ready-mix concrete: Delivered by truck, ideal for large pours. You order by the cubic yard, and the truck mixes on the way.
• Mortar mix: For brick/block work, uses lime and sand, not gravel.

Frequently Asked Questions

How many 80 lb bags of concrete do I need for 1 yard?
An 80-lb bag of pre-mixed concrete yields about 0.6 cu ft. So 27 / 0.6 = 45 bags. For 60-lb bags (0.45 cu ft), you’d need 60 bags.

Is a 94 lb bag of cement 1 cubic foot?
Yes, that’s the standard. A 94-lb bag of portland cement equals 1 cubic foot of loose cement. That’s why the math is simple: 27 cu ft per yard divided by the cement volume.

What does 1:2:4 mean in concrete?
It means 1 part cement, 2 parts sand, and 4 parts gravel by volume. For example, 1 shovelful of cement, 2 of sand, and 4 of gravel.

How much water do I add per bag of cement?
For a 94-lb bag, use about 4.5 to 6 gallons of water (water-cement ratio 0.45–0.60 by weight). Less water gives stronger concrete, but too little makes it unworkable.

Can I use this calculator for mortar?
No, mortar uses lime and has no gravel. For mortar, the ratio is typically 1:3 (cement:sand) with lime added. This calculator is for concrete only.

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in ratio | Mix ratio (cement:sand:gravel) | - | 1:2:4 | 0
in bag | Bag weight | lb | 94 | 0
out bags | Bags of cement per yard | bags | (27 / (1+2+4)) * (1 / 1) * (bag / 94) | 1
out sand | Sand volume | cu ft | (27 / (1+2+4)) * 2 | 1
out gravel | Gravel volume | cu ft | (27 / (1+2+4)) * 4 | 1