5 Inch Concrete Slab - Cement Bags, Sand and Gravel Needed

Concrete volume and materials for any slab or footing

Three measurements turn into a full materials list. Enter the length, width and thickness of your pour, pick a mix strength, and the calculator returns the volume in cubic yards, the number of 94 lb cement bags, tons of sand and tons of gravel. Add local prices and you get a cost breakdown before the first truck arrives.

How to use - step by step

Length - measure the longest side of the pour area in feet. For a perimeter footing, add all four sides together.
Width - measure the perpendicular side in feet. A standard sidewalk is 3-4 ft wide, a two-car driveway is 16-20 ft.
Thickness - enter the slab depth in inches. Sidewalks: 4 in. Driveways: 4-6 in. Footings: 12-24 in.
Mix strength - pick Standard (1:3:5) for light use, Medium (1:2.5:4) for driveways, or Strong (1:2:3) for structural work.
Waste allowance - add 10% for flat slabs, 15% for footings with irregular formwork.
Prices (optional) - fill in local prices for cement bags, sand and gravel to see a total cost estimate.
Read the results - volume in cubic yards, number of cement bags, sand and gravel in tons, plus cost breakdown if prices were entered.

Before and after - what 10% waste allowance actually means

Without waste allowance

A 20 x 12 ft driveway, 5 in thick = 3.70 cu yd. You order exactly that. The subgrade has a low spot, formwork bows slightly, and the finisher needs another quarter yard. The truck left 20 minutes ago.

With 10% waste allowance

Same driveway = 4.07 cu yd. The low spot and formwork flex are covered. You have a small surplus for the mailbox post pad. No short load fee, no emergency second delivery at $200+.

Mix strength reference

Each mix ratio determines how much cement, sand and gravel goes into one cubic yard of concrete.

Mix	Ratio	Cement (bags/cu yd)	Sand (tons/cu yd)	Gravel (tons/cu yd)	Best for
Standard	1:3:5	4.5	0.59	1.01	Sidewalks, patios, garden paths
Medium	1:2.5:4	5.4	0.55	0.97	Driveways, garage slabs
Strong	1:2:3	6.3	0.51	0.93	Footings, columns, structural

Practical examples

Example 1: Sidewalk - 30 x 4 ft, 4 in thick, Standard mix, 10% waste
Volume: 1.63 cu yd | Cement: 8 bags | Sand: 0.96 ton | Gravel: 1.65 tons

Example 2: Two-car driveway - 20 x 18 ft, 5 in thick, Medium mix, 10% waste
Volume: 6.11 cu yd | Cement: 33 bags | Sand: 3.34 tons | Gravel: 5.89 tons

Example 3: Garage slab - 24 x 24 ft, 6 in thick, Medium mix, 10% waste
Volume: 11.73 cu yd | Cement: 64 bags | Sand: 6.41 tons | Gravel: 11.31 tons

Example 4: Strip footing - 100 x 2 ft, 12 in thick, Strong mix, 15% waste
Volume: 8.52 cu yd | Cement: 54 bags | Sand: 4.32 tons | Gravel: 7.92 tons

Example 5: Patio pad - 12 x 10 ft, 4 in thick, Standard mix, 10% waste
Volume: 1.63 cu yd | Cement: 8 bags | Sand: 0.96 ton | Gravel: 1.65 tons

FAQ - Frequently asked questions

How many 80 lb bags of premix equal one cubic yard?

One cubic yard of concrete weighs about 4,050 lb. An 80 lb bag of premixed concrete yields roughly 0.6 cu ft. You need 27 / 0.6 = 45 bags to make one cubic yard. At $5-7 per bag, that is $225-315 per yard - often more expensive than a ready-mix truck delivery ($125-160/cu yd) for pours over 2 cu yd.

When should I order a ready-mix truck instead of mixing bags?

For pours under 1 cu yd, bagged premix is practical. Between 1 and 2 cu yd, it depends on your labor and timeline. Above 2 cu yd, a ready-mix truck is almost always faster and cheaper. Most plants deliver in 8-10 cu yd loads with a short-load surcharge ($50-100) for under 5 cu yd.

How thick should a concrete driveway be?

4 inches is the minimum for passenger cars. If trucks or heavy equipment will use the driveway, go to 5-6 inches. The approach apron (where the driveway meets the street) should be at least 6 inches regardless, because garbage trucks cross it weekly.

What does the waste allowance cover?

Uneven subgrade, formwork flex, spillage, slight over-dig, and the concrete that sticks to the chute. For flat slabs with good formwork, 10% is standard. Footings with stepped bottoms or rocky soil may need 15-20%. Running short mid-pour is far more costly than having a small surplus.

What is the difference between the three mix strengths?

The ratio describes cement:sand:gravel by weight. Standard (1:3:5) uses less cement - fine for sidewalks and patios that carry foot traffic only. Medium (1:2.5:4) adds more cement for vehicle loads. Strong (1:2:3) is the richest mix, used for footings, columns and any element that carries structural loads. Higher cement content means higher cost but also higher compressive strength.

Can I convert the result to pre-mixed bags instead of bulk materials?

Yes. One 80 lb bag of premixed concrete yields about 0.6 cu ft. Divide the total cubic feet by 0.6 to get the number of bags. For a 60 lb bag (0.45 cu ft), divide by 0.45. Example: 44 cu ft / 0.6 = 74 bags of 80 lb premix.

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