How Much Concrete For A 10x10 Slab 4 Inches Thick

Figuring out how much concrete for a 10x10 slab 4 inches thick starts with one honest admission: the answer is a range, not a single number. Concrete volume depends on the exact dimensions you measure, the depth you actually pour, and how much is lost to spillage and an uneven base — and the bag count depends on the bag size and the yield printed on the bag label. This page works through a 10 ft by 10 ft slab, 4 in thick step by step, using the typical yields in our material data, and every result below is shown as a range. The product label governs: if the bag you buy yields a little less than the typical figure, the count goes up, and that is exactly why the range exists.

The calculator on this page asks for the same inputs the worked example uses: the dimensions of a 10 ft by 10 ft slab, 4 in thick, the depth, and the bag size. It returns a range, because the honest answer is a range — the low end assumes a flat base and no spillage, and the high end assumes the usual 10% waste. Plan your order on the high end. A spare bag costs little; a short pour costs a second delivery, a cold joint, and a visible repair.

How the calculation works

The calculator needs the shape of the pour, the depth, and the bag size you plan to buy, and each one changes the answer. For a rectangular pour the volume is length times width times depth, all in feet, divided by 27 to get cubic yards — one cubic yard is 27 cubic feet (0.76 cubic metres). Depth is where most mistakes happen: 4 in (10 cm) is 0.333 ft, 6 in (15 cm) is 0.5 ft, so always convert inches to feet before multiplying. A slab that is 10 ft by 10 ft at 4 in thick is 100 times 0.333, or 33.3 cubic feet, which is about 1.2 cubic yards before waste. The same slab at 6 in thick is half as much again, about 1.9 cubic yards, which is why the thickness in the keyword matters as much as the footprint.

Once the volume is known, it is converted to bags. Our material data gives typical yields of about 45 80 lb (36.3 kg) bags per cubic yard and about 60 60 lb (27.2 kg) bags per cubic yard, because an 80 lb bag yields about 0.6 cubic feet and a 60 lb bag about 0.45 cubic feet — those are typical values, and the bag label on the exact product you buy governs. On top of that, add the typical waste allowance of about 10% for spillage, an uneven subgrade, and the concrete that stays in the mixer and the wheelbarrow. The worked example below shows the low end with no waste and the high end with the full 10% allowance, so you can see the range instead of a single number that pretends the pour will be perfect.

A 10 by 10 slab at 4 in is the classic small-slab example, and it is worth doing carefully because it is the size most people pour first. The volume is 100 square feet times a third of a foot, which is about 33 cubic feet, or about 1.2 cubic yards. At this size the job sits right on the boundary between bagged mix and a ready-mix short load, so price both. If the slab has a thickened edge or a footing around the perimeter, that edge is extra volume on top of the slab itself.

Worked example: a 10 ft by 10 ft slab, 4 in thick

Here is the full arithmetic for a 10 ft by 10 ft slab, 4 in thick.

Step 1 — convert to feet. Length 10 ft. Width 10 ft. Depth 4 in ÷ 12 = 0.333 ft.

Step 2 — volume in cubic feet. 10 × 10 × 0.333 = 33.3 cubic feet.

Step 3 — convert to cubic yards. 33.3 ÷ 27 = 1.23 cubic yards, or about 1.2 cubic yards.

Step 4 — bags, low end. At the typical yield of about 45 80 lb bags per cubic yard: 1.23 × 45 = 55.6 bags, rounded up to 56 bags. With 60 lb bags: 1.23 × 60 = 74.1, rounded up to 75 bags.

Step 5 — bags, high end with the 10% waste allowance. 1.23 × 1.10 = 1.36 cubic yards, or 62 80 lb bags (82 60 lb bags). Order 56–62 80 lb bags and keep one or two spare; a slab that runs short at the far corner leaves a patch that will always show.

Cost guidance

Budgeting for how much concrete for a 10x10 slab 4 inches thick means pricing the range, not a single number. Take the worked-example quantity (1.2–1.4 cubic yards, or about 56–62 80 lb bags) and price it twice: once at the low end of the range and once at the high end, using the current shelf price per bag at the store where you will actually buy, or the per-cubic-yard ready-mix quote from a local supplier. The difference between the two totals is your contingency, and it is usually smaller than the cost of running short mid-pour. Two cost traps catch first-timers: ordering the low end and then paying a second delivery charge for the few bags that finish the job, and forgetting the extras — formwork, stakes, rebar or mesh, a float, and curing compound or plastic sheeting. Compare the total delivered cost, not the per-bag price, and keep one or two unopened bags for patching; an opened bag that gets damp is wasted money.

If the job grows while you measure — a footing that turns out longer than the plan, a sidewalk that needs an extra section — redo the volume from the new dimensions rather than guessing a percentage on top of the old total. Concrete quantities scale with volume, not with length alone, so a small change in depth changes the total more than most people expect. And if you are comparing bagged mix with ready-mix, remember the comparison only works when both quotes cover the same volume including waste, the same delivery distance, and the same extras; a cheap per-bag price with an expensive delivery is not a cheap job.

Step by step: measure, calculate, order

1. Measure twice. Measure the slab length and width in feet, and the depth in inches at four or more places across the base. Measure each run separately — a footing that turns a corner is two runs, not one — and write every dimension down in feet and inches before you convert anything.

2. Convert and calculate. Convert inches to feet (divide by 12), then apply the volume formula for your shape: length times width times depth divided by 27 for a rectangle, or pi times radius squared times depth for a round tube or post hole. Use the calculator on this page to check your arithmetic, and run it twice with the low and high depth if your excavation is uneven.

3. Add waste and round up. Add the typical 10% waste allowance for spillage and an uneven subgrade, then round up to whole bags or to the nearest quarter cubic yard for a truck. A bag cannot be bought in fractions, and a pour that stops short is far more expensive than one spare bag.

4. Order and check the delivery. Order the high end of the bag range below, all the same mix, all the same product and mix, and check the bag labels against the yields the calculator assumed. If you are ordering ready-mix, confirm the slump, the mix strength and the delivery window, and make sure the truck can reach the pour.

5. Before you pour. Set and brace the forms, check the depth with a straightedge in several places, wet the subgrade lightly so it does not steal water from the mix, and have your screed, float and curing cover within reach. Concrete waits for nobody once it is mixed.

Common mistakes to avoid

Three mistakes ruin more small concrete jobs than anything else. First, using the nominal depth instead of the real one — a slab formed with 2x4s is often poured a little deeper than 4 in once the base settles, so measure after the base is compacted. Second, mixing bag counts from two different bag sizes: 80 lb and 60 lb bags yield different volumes, so pick one size and do all the arithmetic in that size. Third, pouring without a plan for finishing and curing — concrete that dries too fast cracks, and concrete that is not screeded level cannot be fixed later. Have the tools, the help and the curing cover ready before the first bag is mixed, and never add extra water to make a stiff mix easier to place; it weakens the finished pour.

Frequently asked questions

How much concrete do I need for a 10x10 slab 4 inches thick?

Multiply length times width times depth and divide by 27. A 10 ft by 10 ft slab at 4 in thick is 33.3 cubic feet, or about 1.2 cubic yards before waste — 1.2–1.4 cubic yards with the typical 10% allowance, or 56–62 80 lb bags.

How many 80 lb bags for a 10x10 slab?

At the typical yield of about 45 80 lb bags per cubic yard, a 10 by 10 slab at 4 in thick needs 56–62 80 lb bags, including the 10% waste allowance. With 60 lb bags the count is 75–82 bags. Pick one bag size and do all the arithmetic in that size.

Should I order ready-mix for a 10x10 slab?

At about 1.2 cubic yards, both are practical. Bagged mix means about 56–62 80 lb bags to mix by hand or in a rented mixer, which is a long day for one person. A ready-mix short load delivers the same volume in one truck, usually with a short-load charge — price both against the same volume including waste and compare the delivered totals.

How thick should a 10x10 slab be?

About 4 in is common for a shed base or a patio slab that carries foot traffic and light loads. A slab that will carry a vehicle needs to be thicker, about 5–6 in, with reinforcement. Check local code for the minimum thickness in your area; the code governs, and a thin slab cracks under loads it was not designed for.

What base do I need under a 10x10 slab?

A compacted gravel base, usually about 4 in of compacted crushed stone, gives the slab something stable to sit on and helps drainage. The base is not part of the concrete volume, but a base that is not compacted will settle, and the slab will crack as it follows the base down. Compact in layers and check the level before you set the forms.

Related calculators

Results are estimates — verify with the product label. Coverage, pack sizes, yields and prices vary by brand, product line, surface and region; the label on the product you buy governs. Cost figures are typical retail ranges — check the current shelf price before budgeting.