How Many Bags of Concrete for a Small Pad?

Updated November 1, 2026

A small pad is often a bag job. Length, width, and thickness still make a volume in cubic feet. You then divide that volume by the yield printed on the bag and round up to whole bags. Ready-mix plants sell cubic yards, usually in quarter-yard steps. The Concrete Calculator stops at yards. It does not count bags.

Measure the pad inside the forms

Measure length and width in feet, to the inside of the forms. That is the concrete you will place. Thickness for a shed pad or a landing is often 4 inches. Write the thickness in inches if that is how you measured it, then divide by 12 before you multiply. Four inches is 4 ÷ 12 of a foot.

One rectangle is one calculation. This page is that rectangle. A post hole is a cylinder. A continuous footing is a trench. Neither one is a flat pad, and neither one belongs in the bag count below. If the project is a fence post, start from the fence length and the hole, not from this slab.

A 4 by 4 foot pad at 4 inches

One pad, 4 feet by 4 feet, 4 inches thick.

• Thickness in feet: 4 ÷ 12.
• Cubic feet: 4 × 4 × (4 ÷ 12) = 5.33 cu ft.
• Cubic yards: 5.33 ÷ 27 = 0.20 cu yd.

There are 27 cubic feet in a cubic yard. 5.33 cubic feet is the concrete in the forms with nothing extra. 0.20 cubic yards is the same box in the unit a ready-mix plant uses. The calculator shows both of those figures when you enter 4 feet, 4 feet, and 4 inches, with quantity set to 1.

Divide by the yield on the bag

Bag math is cubic feet divided by the cubic feet one bag is supposed to make. The number is on the bag. These two yields are common examples. If your bag prints a different yield, use that yield.

• An 80 lb bag is often labeled near 0.60 cubic feet. 27 ÷ 0.60 = 45 bags per cubic yard.
• A 60 lb bag is often labeled near 0.45 cubic feet. 27 ÷ 0.45 = 60 bags per cubic yard.

Before waste, the full 4 × 4 × (4 ÷ 12) is 5.333… cubic feet, which the calculator shows as 5.33. Divided by 0.60 that is 8.89, so 9 of the 80 lb bags if you round up with no allowance. Divided by 0.45 it is 11.85, so 12 of the 60 lb bags. Those counts assume every bag hits the yield on the label and the forms are exact. They are the floor, not the order.

Add waste, then round up to a whole bag

Waste is extra mix so the pad can finish level. It is not a bag you expect to return unopened. The calculator accepts 0, 5, 10, 15, or 20 percent, and it applies that percent to the cubic yards. The same percent on the cubic feet is the number you divide by the bag yield.

• 5% — one rectangle, square forms, and a base you have already checked with a straightedge.
• 10% — the usual small pad. The full 5.333… cubic feet times 1.10 is 5.87 cubic feet.
• 15% or 20% — forms that are out of square, or a base that still has low spots.

At 10 percent:

• 80 lb example: 5.87 ÷ 0.60 = 9.78, which rounds up to 10 bags. Ten bags at 0.60 cubic feet are 6.00 cubic feet.
• 60 lb example: 5.87 ÷ 0.45 = 13.04, which rounds up to 14 bags. Fourteen bags at 0.45 cubic feet are 6.30 cubic feet.

You cannot buy nine-tenths of a bag. Stopping at 9 of the 80 lb bags leaves you under the 5.87 cubic feet you just allowed for. Mix to the water printed on the bag. Extra water makes the batch easier to push and usually yields less than the label.

The same pad in cubic yards

Enter the same 4 by 4 by 4 inches in the concrete calculator with 10 percent waste. It reports 0.20 cubic yards exact, 0.22 cubic yards with waste, and a recommended ready-mix order of 0.25 cubic yards. A quarter yard is 0.25 × 27 = 6.75 cubic feet.

That quarter yard is a little more concrete than the 10-bag or 14-bag stack, and it is still a short load. Plants often add a fee below their minimum, commonly around one yard. The yard-scale walk-through, including the quarter-yard round-up on a 10 by 12 foot slab, is How Much Concrete Do I Need for a Slab?. For this 4 by 4 pad, the bag count is the purchase that matches the volume.

What the bag count leaves out

The 10 bags or 14 bags are concrete only. Gravel under the pad, rebar or mesh, and form boards are separate. A post hole or a footing is a different shape, so do not stretch this pad into a fence. If you type a price per cubic yard into the calculator, that cost line prices the 0.25 yard ready-mix order. It does not price bags, a short-load fee, or tax.