The formula: yield divided by thickness
A bag of concrete mix does not cover an area by itself. It makes a volume of mixed concrete, and the area that volume fills depends on how thick you pour it. The manufacturer states that volume as the yield, so coverage is the yield divided by the thickness, with both in feet.
For an 80 lb bag at 0.6 ft³ and a 4 in thickness, 4 ÷ 12 = 0.3333 ft, and 0.6 ÷ 0.3333 = 1.8 ft². Doubling the thickness halves the area, so the same bag covers 3.6 ft² at 2 in and 1.2 ft² at 6 in.
Coverage by bag size and thickness
These figures use the yields in QUIKRETE's datasheet for Concrete Mix No. 1101, which states them as approximate. The datasheet says the mix is designed for pouring concrete 2 in (50 mm) thick or more, so the table starts at 2 in. The thicknesses show how the arithmetic behaves. They are not a suggestion for what your project needs, which comes from your plans.
| Bag size | Yield (ft³) | 2 in thick | 3 in thick | 4 in thick | 5 in thick | 6 in thick |
|---|---|---|---|---|---|---|
| 90 lb bag | 0.675 | 4.05 | 2.7 | 2.025 | 1.62 | 1.35 |
| 80 lb bag | 0.6 | 3.6 | 2.4 | 1.8 | 1.44 | 1.2 |
| 60 lb bag | 0.45 | 2.7 | 1.8 | 1.35 | 1.08 | 0.9 |
| 50 lb bag | 0.375 | 2.25 | 1.5 | 1.125 | 0.9 | 0.75 |
| 40 lb bag | 0.3 | 1.8 | 1.2 | 0.9 | 0.72 | 0.6 |
Metric: square metres per bag
The datasheet lists the 80 lb yield as 0.6 ft³ (17 L). In metric, divide the yield in cubic metres by the thickness in metres. An 80 lb bag is 0.017 m³, so at 10 cm it covers 0.017 ÷ 0.10 = 0.17 m². The conversion uses the exact definition 1 in = 25.4 mm.
| Bag size | Yield (m³) | 5 cm thick | 10 cm thick | 15 cm thick |
|---|---|---|---|---|
| 90 lb bag | 0.0191 | 0.382 | 0.191 | 0.127 |
| 80 lb bag | 0.017 | 0.34 | 0.17 | 0.113 |
| 60 lb bag | 0.0127 | 0.255 | 0.127 | 0.085 |
| 50 lb bag | 0.0106 | 0.212 | 0.106 | 0.071 |
| 40 lb bag | 0.0085 | 0.17 | 0.085 | 0.057 |
From an area to a number of bags
To order, work the other way. Area times thickness gives the volume. Add the allowance you choose, divide by the yield, and round up once on the total rather than per section. The table applies a 10% allowance. That figure is a placeholder to show the arithmetic, not a recommendation: uneven ground, forms and spillage decide the real number for your job.
| Project | Area | Thickness | Planning volume (ft³) | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 3 × 8 ft walkway | 24 ft² | 4 in | 8.8 | 15 | 20 |
| 10 × 10 ft slab | 100 ft² | 4 in | 36.7 | 62 | 82 |
| 4 × 5 ft pad | 20 ft² | 6 in | 11 | 19 | 25 |
| 1.5 × 1 m area (metric) | 1.5 m² | 10 cm | 5.8 | 10 | 13 |
The reverse question: how much area do my bags cover?
If you already own the bags, multiply the number of bags by the yield and divide by the thickness. Twenty 60 lb bags at 0.45 ft³ make 9 ft³, which is 27 ft² at 4 in. Holding back a 10% reserve for spillage and an uneven base leaves about 24.5 ft² that you can plan on.
Why a 60 lb bag from one brand covers more than another's
Yield is a property of the product, not of the bag weight. QUIKRETE's datasheet gives 0.45 ft³ for a 60 lb bag of Concrete Mix No. 1101. Rapid Set's datasheet for its CONCRETE MIX gives about 0.5 ft³ for its 60 lb bag. At 4 in thick that is 1.35 ft² against 1.5 ft², about 11% more area from the same bag weight.
These are different products. Rapid Set's is a fast-setting mix whose datasheet lists thicknesses from 2 in to 24 in, so this compares yields only and says nothing about which suits a job. The practical point is that a "bag covers" figure from a website is only as good as the yield of the exact product you buy.
| Product | Stated yield (ft³) | Square feet at 4 in |
|---|---|---|
| QUIKRETE Concrete Mix No. 1101, 60 lb | 0.45 | 1.35 |
| Rapid Set CONCRETE MIX, 60 lb | 0.5 | 1.5 |
A small change in thickness changes the bag count
A 10 × 10 ft area (100 ft²) at 4 in needs 62 bags of 80 lb with a 10% allowance. At 4.5 in it needs 69, at 5 in 77, and at 6 in 92. A half inch across the whole area is worth about 7 bags here, so measure the thickness you will actually pour, including where the ground dips below the form line.
What coverage figures leave out
A coverage number is geometry plus a stated yield. It does not include:
- An uneven base or forms that are not level, which take more concrete than the nominal thickness.
- Spillage, material left in the mixer or wheelbarrow, and bags that are not used to the last scoop.
- Any difference between the stated yield and what your batch actually makes. Both datasheets say "approximately".
- The thickness, base, reinforcement and strength your project needs. This article does not set those; use your plans and a qualified professional.
When bags stop being practical
Coverage per bag is most useful on small jobs. At 4 in an 80 lb bag covers 1.8 ft², so a 10 × 10 ft slab takes 62 bags, which is about 1.5 pallets at the 42 bags per pallet QUIKRETE lists for 80 lb bags. One cubic yard (27 ft³) takes 45 bags of 80 lb. For larger pours, compare bags with ready-mix using your own supplier quotes.
Common questions
How much does an 80 lb bag of concrete cover?
About 1.8 square feet at 4 inches thick, using QUIKRETE's approximate yield of 0.6 ft³ for Concrete Mix No. 1101. It covers 3.6 ft² at 2 inches and 1.2 ft² at 6 inches. Another product can yield a different volume, so use the figure printed on your bag.
How much does a 60 lb bag of concrete cover?
About 1.35 square feet at 4 inches thick for QUIKRETE Concrete Mix No. 1101 (0.45 ft³). Rapid Set's datasheet gives about 0.5 ft³ for its 60 lb bag, which covers 1.5 ft² at the same thickness.
How much does a 50 lb bag of concrete cover?
About 1.125 square feet at 4 inches thick, from QUIKRETE's approximate yield of 0.375 ft³. At 2 inches it covers 2.25 ft².
How many bags of concrete do I need for a 10 × 10 slab?
At 4 inches thick with a 10% allowance, a 10 × 10 ft slab needs 62 bags of 80 lb at 0.60 ft³ per bag, or 82 bags of 60 lb. The thickness and allowance are example inputs. Enter your own in the bag calculator.
How many square feet does a cubic yard of concrete cover?
It depends on the thickness. A cubic yard is 27 cubic feet, so it covers 324 ÷ thickness in inches square feet, which is 81 square feet at 4 inches and 54 at 6 inches. The cubic feet to cubic yards calculator has the full depth table.
Does the amount a bag covers change with thickness?
Yes, in inverse proportion. A bag makes a fixed volume of concrete, so pouring it half as thick covers twice the area, and pouring it twice as thick covers half.
Is the coverage printed on the bag exact?
No. Manufacturers state yield as approximate, and a real batch can differ from it. Use the stated yield to plan, add an allowance you choose, and check the label of the product you buy.
Do I need to buy extra bags?
Most jobs lose some material to an uneven base, spillage and mixing. The amount is your decision from your site conditions, and the calculator shows the allowance separately from the net quantity so you can see how much of an order it is.
Sources and further reading
- QUIKRETE Concrete Mix No. 1101 datasheet ↗Read directly, October 19, 2026. States yields of approximately 0.30, 0.375, 0.45, 0.60 and 0.675 ft³ for the 40, 50, 60, 80 and 90 lb bags, and that the mix is designed for pouring concrete 2 in (50 mm) thick or more.
- Rapid Set CONCRETE MIX datasheet (CTS Cement) ↗Read directly, October 19, 2026. States that one 60 lb bag yields approximately 0.5 ft³ (0.01 m³) and that the mix is applied in thicknesses from 2 in to 24 in.
- QUIKRETE Concrete Mix No. 1101 product page ↗Read directly, October 19, 2026. Lists 42 bags of 80 lb, 56 of 60 lb and 80 of 40 lb per pallet; it gives no count for the 50 or 90 lb bags.
- NIST: SI Units – Length ↗Basis for the exact inch-to-centimetre conversion used in the metric table (1 in = 25.4 mm).
This article is general quantity-planning information. Confirm product requirements, project specifications, and local rules with the appropriate supplier or qualified professional.