Concrete Mix Calculator
Calculate exact quantities of cement, sand, gravel, and water needed to make concrete from scratch. Enter the volume needed and select your mix ratio.
Materials Needed
Cement (94lb bags)
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Sand (cubic feet)
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Gravel (cubic feet)
0
Water (gallons)
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Understanding Concrete Mix Ratios
The ratio represents Cement : Sand : Gravel by volume. A 1:2:3 mix means for every 1 part cement, you add 2 parts sand and 3 parts gravel.
Mix Ratio Guide
| Ratio | Strength | Best For |
|---|---|---|
| 1:2:3 | 2500-3000 PSI | Slabs, sidewalks, general use |
| 1:1.5:3 | 3500-4000 PSI | Driveways, structural footings |
| 1:2:4 | 2000-2500 PSI | Foundation bases, mass pours |
| 1:3:6 | 1000-1500 PSI | Blinding, leveling, non-structural |
Water-to-Cement Ratio
The standard water-to-cement ratio is 0.45-0.55 by weight. Too much water weakens concrete; too little makes it unworkable. Aim for a consistency like thick oatmeal — holds its shape but flows when vibrated.
When to Mix From Scratch vs Buy Bags
- Buy premixed bags for projects under 1 cubic yard — more consistent, easier
- Mix from scratch for large projects or when you need a specific ratio not available in bags
- Order ready-mix truck for anything over 2 cubic yards
Concrete Mix FAQ
What is the best concrete mix ratio for a slab?
The standard 1:2:3 ratio (1 part cement, 2 parts sand, 3 parts gravel) produces 2500-3000 PSI concrete that's suitable for most residential slabs, sidewalks, and patios. For driveways and garages needing 3500-4000 PSI, use a richer 1:1.5:3 mix. For most DIYers, pre-mixed bags are easier and more consistent than mixing from scratch.
How much water should I add to concrete?
The ideal water-to-cement ratio is 0.45-0.55 by weight. For a standard 80lb bag, that's about 3.5-4 quarts of water. The mix should have a thick oatmeal consistency — it holds its shape when scooped but flows when vibrated. Adding too much water is the #1 DIY mistake: it makes concrete easier to pour but dramatically weakens the final product.
When should I mix concrete from scratch vs buy bags?
Buy pre-mixed bags for projects under 1 cubic yard — they're pre-proportioned, consistent, and eliminate measuring errors. Mix from scratch only when: you need a specific ratio not available in bags, you're doing a very large pour (3+ yards) where a mixer truck isn't available, or you need specialty aggregate. For most residential projects, bags or ready-mix delivery are more practical and consistent.