Cement Calculator

For a residential driveway, use a 1:2:4 (standard) mix ratio, which produces approximately 3,000 PSI concrete. This is adequate for passenger vehicles. If the driveway will support heavy trucks or equipment, step up to 1:1.5:3 (strong) for roughly 4,000 PSI. Driveways should be at least 4 inches thick (5–6 inches at the apron where it meets the street) and reinforced with fiber mesh or #4 rebar at 18-inch spacing.

The general rule is about 5 gallons of water per 94-lb bag of Portland cement for a standard mix. However, the actual amount depends on aggregate moisture content and desired slump. Too much water is the most common mistake in site-mixed concrete — it weakens the finished product. A 0.45 water-to-cement ratio (by weight) produces strong, durable concrete. The mix should hold its shape when slumped, not flow like soup. If it seems too stiff, add water in half-gallon increments only.

Cement is a powder (Portland cement) that acts as the binding agent. Concrete is the finished product made by mixing cement with sand (fine aggregate), gravel or crushed stone (coarse aggregate), and water. Cement typically makes up 10–15% of a concrete mix by volume. This calculator helps you determine how much of each ingredient you need to produce a given volume of concrete. When someone says “a bag of cement,” they mean a 94-lb bag of Portland cement powder, not pre-mixed concrete (which is sold separately as 60-lb or 80-lb bags of ready-to-use mix).

For a standard 1:2:4 mix, you need approximately 6 bags of Portland cement per cubic yard of finished concrete. A stronger 1:1.5:3 mix requires about 7–8 bags per cubic yard. A lean 1:3:6 mix uses approximately 4 bags per cubic yard. These numbers account for the dry-to-wet volume conversion factor (1.54x) because dry ingredients compact when mixed with water. The calculator above applies this factor automatically.