What is the concrete mix ratio for a slab?
A typical concrete mix is 1 part portland cement, 2 parts sand and 3 parts gravel by volume, per Quikrete’s Portland Cement data sheet. For half a cubic yard that is about 3 bags of 94 lb cement.
How to work it out
- 0.5 cu yd × 5.5 bags of 94 lb per cubic yard = 259 lb of cement
- ÷ 94 lb per bag = 3 bags
- Mix: 1 part cement : 2 parts sand : 3 parts gravel (Quikrete Portland Cement data sheet)
The 1:2:3 ratio is the classic general-purpose mix for slabs, walks and footings when you mix from raw materials. It is measured by volume — buckets or shovelfuls — not by weight.
Adjust for your project
- Weight of cement
- 259 lb
- Mix by volume
- 1 part cement : 2 parts sand : 3 parts gravel
- Or premixed 80 lb concrete bags
- 23 bags
- Buy clean concrete sand and gravel meeting ASTM C33 (Quikrete’s spec for this mix) — the yard may sell them in bulk or in bags. Measure each part with the same bucket, and use the least water that gives a workable mix: extra water weakens concrete.
Cement for small batches (5½ bags per yard)
| Concrete to make | Cement bags | Weight of cement | Or premixed 80 lb concrete bags |
|---|---|---|---|
| 0.1 cu yd | 1 bag | 52 lb | 5 bags |
| 0.25 cu yd | 2 bags | 129 lb | 12 bags |
| 0.5 cu yd | 3 bags | 259 lb | 23 bags |
| 0.75 cu yd | 5 bags | 388 lb | 34 bags |
| 1 cu yd | 6 bags | 517 lb | 45 bags |
How to use 1:2:3
Pick one container and use it for everything. For a mixer batch, that might be one 5 gallon bucket of cement, two of sand and three of gravel. Mix them dry, then add water gradually until the concrete is stiff but workable. Every extra splash of water makes the concrete weaker and more prone to cracking, so resist making it soupy to ease placing.
For a ready-mix order, the plant designs the mix for you by strength (for example 3,000 or 4,000 psi) rather than by ratio. NRMCA notes specified strengths of 3,500 to 5,000 psi are typical; tell the plant what you are pouring and let them recommend the mix.
Other mixes from the same cement
Mortar and stucco use more sand and no gravel, plus lime. Quikrete’s sheet lists Type S mortar at 1 part cement, ½ part hydrated lime and 3½–4½ parts masonry sand, and scratch and brown coat stucco at 1 part cement, ½ part lime and 4½–6 parts plaster sand. For how much cement a whole yard needs, see how many bags of cement in a yard of concrete; for premixed bags, how much does an 80 lb bag of concrete cover.
Different size? Use the full Cement Calculator (Mix Your Own).
What you’ll need
- Portable electric concrete mixerPremium price
A small drum mixer turns a long day of hand-mixing into batches of two or three 80 lb bags. Check the drum size against the bag count you need.
See options on Amazon (opens in a new tab) - Mortar and concrete mixing tubBudget price
A wide, shallow tub for one or two bags at a time — easier to clean and to pull a hoe through than a wheelbarrow.
See options on Amazon (opens in a new tab) - Mortar hoeBudget price
The holes in the blade pull water through dry mix, so bagged concrete and mortar mix evenly without dry pockets.
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Frequently asked questions
How many bags of cement for a quarter yard of concrete?
2 bags of 94 lb (about one and a half), mixed 1:2:3 with sand and gravel.
How many bags of cement for 2 yards at six bags per yard?
12 bags of 94 lb, about 1,128 pounds of cement.
Other common sizes
- How many bags of cement in a yard of concrete — 5 to 6 bags of 94 lb portland cement (or 45 bags of 80 lb concrete mix)
Sources
- Quikrete Portland Cement data sheet (opens in a new tab) — Concrete mix 1 part cement : 2 parts sand : 3 parts gravel by volume; five to six 94 lb bags of cement per cubic yard of concrete; Type S and Type N mortar and ASTM C926 stucco blends.
- Quikrete Concrete Mix (No. 1101) data sheet (opens in a new tab) — Yields: 40 lb ≈ 0.30, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60, 90 lb ≈ 0.675 cu ft; unit weight ≈ 140 lb/cu ft; for pours 2 in thick or more; 6–9 pints of water per 80 lb bag; control joints every 6–8 ft; cure 5 days at 70 °F or above, 7 days at 50–70 °F; protect from freezing for 48 hours.
- OSHA 3351 — Preventing Skin Problems from Working with Portland Cement (opens in a new tab) — Wet portland cement can cause caustic burns that may not hurt at first and in severe cases reach the bone.