Cubic Feet Per Bag of Cement: Sizes & Yields

This calculator works out the volume of concrete, mortar, or mix you get from a bag of cement, based on the bag’s weight and the mix ratio you plan to use. Enter the bag size in pounds or kilograms, choose the mix ratio (like 1:2:4 for concrete), and you’ll get the cubic feet of finished material, plus the yield in cubic yards and the number of bags you need per cubic yard. The first result shown is the cubic feet per bag, which is what most DIYers and contractors need to plan a pour.

Formula

The standard rule for a 94-pound bag of Portland cement is that it contains exactly 1 cubic foot of cement. So the cement volume in cubic feet is:

Cement volume (ft³) = bag weight (lb) ÷ 94

But that’s just the cement. To get the total volume of mixed concrete or mortar, you need to account for the other ingredients. For a concrete mix with parts cement : sand : gravel (by volume), the total volume of dry materials is:

Total dry volume = cement volume × (sum of all parts)

However, when water is added, the mix shrinks by about 25–30% because the fine particles fill the voids between the larger aggregates. A common practical factor is 1.5: the dry volume of a 1:2:4 mix (1+2+4 = 7 parts) yields about 2/3 of that volume as wet concrete. So the final formula becomes:

Cubic feet per bag = (bag weight ÷ 94) × (27 ÷ total parts) × 1.5

Where:

• bag weight – weight of one bag of cement in pounds (94 lb is standard, but 80 lb, 60 lb, 50 lb, 40 lb are common for premixed bags)
• total parts – sum of the ratio numbers (e.g., 1+2+4 = 7 for a 1:2:4 mix)
• 27 – number of cubic feet in one cubic yard
• 1.5 – yield factor (accounts for shrinkage and voids; actual yield varies with water content and aggregate size)

Worked Example

Using the default values – a 94 lb bag and a 1:2:4 mix:

1. Cement volume = 94 ÷ 94 = 1 ft³
2. Total parts = 1 + 2 + 4 = 7
3. Dry volume = 1 × 7 = 7 ft³
4. Wet yield = 7 × (1.5 ÷ 27) = 7 × 0.05556 = 0.3889 yd³
5. Cubic feet per bag = 0.3889 × 27 = 10.5 ft³

The calculator shows 10.50 ft³ for the first output. That means one 94 lb bag of cement, mixed with 2 parts sand and 4 parts gravel, produces about 10.5 cubic feet of wet concrete – enough for a 4-inch-thick slab roughly 3.15 square feet (about 1.8 ft × 1.8 ft).

Why Bag Size Matters

Not all cement bags are the same. The most common sizes you’ll find are:

• 94 lb (42.6 kg) – the standard full bag of Portland cement, exactly 1 ft³ of cement.
• 80 lb (36.3 kg) – common for premixed concrete (already contains sand and gravel).
• 60 lb (27.2 kg) – popular for smaller projects, easier to handle.
• 50 lb (22.7 kg) – often used for mortar or repair mixes.
• 40 lb (18.1 kg) – small bags for patch work or thin overlays.

For pure Portland cement, the volume per bag is directly proportional to weight: a 47 lb bag holds 0.5 ft³, a 23.5 lb bag holds 0.25 ft³, and so on. But when you buy a “concrete mix” bag, the cement is already blended with aggregates, so the bag’s weight includes those materials – the yield per bag is much smaller than pure cement.

How to Use This Calculator

Follow these steps to get accurate results:

1. Enter the bag weight in pounds (or convert from kg: 1 kg = 2.20462 lb).
2. Enter the mix ratio as three numbers separated by colons, e.g., 1:2:4 for concrete, 1:3 for mortar (omit the third number if no gravel).
3. Read the cubic feet per bag – this is the wet volume of concrete or mortar you’ll get.
4. Check the bags per cubic yard – that tells you how many bags to buy for a yard of concrete.

For example, if you’re pouring a small patio slab that’s 10 ft × 10 ft × 4 in thick, the volume is (10 × 10 × 0.333) = 33.3 ft³. With a 94 lb bag of cement and a 1:2:4 mix, each bag yields 10.5 ft³, so you’d need about 3.2 bags – round up to 4 bags. If you’re using 80 lb premix bags, each yields about 0.6 ft³ (check the bag label), so you’d need 56 bags.

Common Mistakes and Misconceptions

Mistake 1: Confusing cement with concrete. Cement is just one ingredient in concrete. A bag of cement is not a bag of concrete. The calculator above is for pure cement plus your own sand and gravel. If you’re using a premix bag, the yield is printed on the bag – typically 0.45 to 0.60 ft³ per 80 lb bag, depending on the mix.

Mistake 2: Ignoring shrinkage. Many people multiply the dry volumes directly, forgetting that water reduces the total volume. The 1.5 factor is a rule of thumb – actual yield can vary from 1.4 to 1.6 depending on how much water you add and the aggregate size. Too much water increases shrinkage and reduces strength.

Mistake 3: Using the wrong ratio. The 1:2:4 mix is a common general-purpose concrete (about 3000 psi). But for footings you might use 1:2.5:3.5, for slabs 1:2:4, for high-strength 1:1.5:3. Always check your project specs.

Mistake 4: Rounding too early. If you round the cubic feet per bag to 10 instead of 10.5, you’ll under-order by 5% – that can leave you short on a big pour. Always round up to the nearest whole bag.

Cost and Quantity Planning

While prices vary by region and brand, the key cost factor is the number of bags. For a 1:2:4 mix, you need:

• 1 part cement – 1 bag (94 lb) per 10.5 ft³ of concrete
• 2 parts sand – about 2 × 94 lb = 188 lb of sand (roughly 2.2 ft³)
• 4 parts gravel – about 4 × 94 lb = 376 lb of gravel (roughly 4.4 ft³)

So for 1 cubic yard (27 ft³) of concrete, you’d need about 2.6 bags of cement, 5.2 ft³ of sand, and 10.4 ft³ of gravel. In practice, you’d buy 3 bags of cement, 6 ft³ of sand, and 11 ft³ of gravel, plus water. The calculator’s “bags per cubic yard” output gives you that number directly – 2.6 bags for the default.

Safety and Handling

Portland cement is caustic. When dry, it can irritate eyes and lungs; when wet, it can cause severe skin burns. Follow these safety practices:

• Wear gloves, long sleeves, and eye protection when handling cement or concrete mix.
• Use a dust mask or respirator when mixing dry cement – avoid breathing the dust.
• If cement gets on your skin, rinse immediately with clean water for at least 15 minutes. Do not use solvents.
• If it gets in your eyes, flush with water for 15 minutes and seek medical attention.
• Keep cement dry until you’re ready to use it – moisture causes it to set prematurely.
• Dispose of unused mix according to local regulations – never pour wash water down storm drains.

Alternatives to Traditional Cement

If you’re looking for a different material, consider these options:

• Pre-mixed concrete – just add water; the bag already has the right proportions. Yield per bag is printed on the label.
• Mortar mix – a blend of cement, lime, and sand, used for brick and block work. Yields about 0.5 ft³ per 80 lb bag.
• Quikrete or similar – brand-name mixes that include aggregates; not pure cement. Always check the specific product’s yield.
• Lime mortar – for historic restoration, softer and more breathable.
• Geopolymer or fly ash concrete – lower carbon footprint, but not widely available for DIY.

For most home projects, a standard 94 lb bag of Portland cement plus your own aggregates is the most economical. Pre-mixed bags cost more per cubic foot but are more convenient for small jobs.

Frequently Asked Questions

How many cubic feet does a 94 lb bag of cement make?
A 94 lb bag of pure Portland cement contains 1 cubic foot of cement. When mixed with sand and gravel in a 1:2:4 ratio, it yields about 10.5 cubic feet of wet concrete. If you’re using a premix bag, the yield is much less – typically 0.45 to 0.60 ft³ per 80 lb bag.

How many 80 lb bags of concrete do I need for 1 cubic yard?
An 80 lb bag of premix concrete yields about 0.60 ft³. Since 1 cubic yard is 27 ft³, you’d need 27 ÷ 0.60 = 45 bags. This varies slightly by brand – check the bag label for exact yield.

What is the difference between cement and concrete?
Cement is a binding powder (usually Portland cement) that, when mixed with water, forms a paste. Concrete is the finished material that also includes sand and gravel (aggregates). A bag of cement is just the powder; a bag of concrete mix already contains the aggregates.

Does the mix ratio affect the cubic feet per bag?
Yes. A 1:2:4 mix (cement:sand:gravel) yields more volume than a 1:1.5:3 mix because the latter has less aggregate. More aggregate means more total volume per bag of cement, but also lower strength. The calculator lets you adjust the ratio to see the difference.

How much water do I add to a 94 lb bag of cement?
For a 1:2:4 mix, you typically use about 6 to 7 gallons of water per bag. The exact amount depends on the moisture content of the sand and gravel. Add water gradually until the mix is workable but not soupy – a good rule is about 0.5 gallons per 10 lb of cement, but always follow the mix design.

Can I use this calculator for mortar?
Yes. For mortar, use a ratio like 1:3 (cement:sand) and omit the gravel – enter 1:3:0. The calculator will give the yield for that mix. Mortar yields are typically smaller because there’s no coarse aggregate.

Related

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in w | Bag weight | lb | 94 | 0
in r | Mix ratio (cement:sand:gravel) | - | 1:2:4 | 0
out vol | Cubic feet per bag | ft³ | (w / 94) * (27 / (1 + 2 + 4)) * 1.5 | 2
out bags_per_yd | Bags per cubic yard | bags | 27 / vol | 1
out cement_ft3 | Cement volume in bag | ft³ | w / 94 | 2