Concrete Bag Calculator
A 10×10 slab at 4 inches thick takes 59 × 80 lb bags, which is where the form opens, with the usual 5% waste. That is 1.30 yd³, already past the point where a short load of ready-mix costs about the same and hands you back a Saturday. Pick your own shape and dimensions below; every count matches the yield printed on the bag.
Bag counts are rounded up. Yields per bag: 80 lb → 0.60 ft³ · 60 lb → 0.45 ft³ · 50 lb → 0.375 ft³ · 40 lb → 0.30 ft³ (check your bag's printed yield).
Bags by project
Slab calculator
Patios, shed bases, driveways, with thickness guidance and common-size chart.
Fence post calculator
Bags per post for any hole size, including fast-setting mix.
Sonotube calculator
Bags per tube for deck footings and pier foundations.
Deck footing calculator
Bags per footing set, with bell-base and post-displacement options.
How many bags of concrete in a yard
45 of the 80 lb bags. Two-way converter plus the chart from ¼ yard to 5 yards.
The rest of the slab: base, steel and thickness
Concrete is the middle layer of the job, not the whole of it. The gravel under the slab and the steel inside it decide whether it cracks, and both get bought by the yard or the stick rather than by the bag. These three take the same dimensions you just typed in.
How much gravel under a slab
Cubic yards, tons and landscape bags of crushed-stone base for pads, patios and driveways.
How much rebar for a slab
Bars each way, linear feet, 20 ft sticks, tie wire and mesh sheets for the grid you pick.
How thick should a slab be
4 inches for patios, 5 to 6 where vehicles park, and what each inch costs you in material.
Quick reference
| Bag size | 80 lb | 60 lb | 50 lb | 40 lb |
|---|---|---|---|---|
| Yield per bag | 0.6 ft³ | 0.45 ft³ | 0.375 ft³ | 0.3 ft³ |
| Bags per cubic yard | 45 | 60 | 72 | 90 |
| Sq ft covered at 4" thick | 1.8 | 1.4 | 1.1 | 0.9 |
Full yield tables, coverage by thickness, and bags on a pallet are in the yields guide. Convert a ready-mix quote with the yard converter. Past about half a yard, run the bags vs ready-mix break-even before you commit a Saturday to the mixer.
FAQ
How many bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet, so: 45 × 80 lb bags, 60 × 60 lb bags, 72 × 50 lb bags, or 90 × 40 lb bags. The full chart and two-way converter live on how many bags of concrete in a yard. If a project needs a yard or more, price ready-mix delivery: 45 bags is over 1.8 tons of material to haul, mix and place before any batch starts setting.
How many bags of concrete do I need for a 10×10 slab?
At the standard 4-inch thickness, a 10×10 slab is 33.3 ft³, about 56 bags of 80 lb concrete before waste, 59–62 with 5–10% waste. That's firmly in ready-mix territory (about 1.25 yd³): a short-load truck usually costs about the same as the bags and saves you a punishing day of mixing.
How much does one 80 lb bag of concrete cover?
An 80 lb bag yields 0.60 ft³: enough for 1.8 square feet at 4 inches thick, or a single 8-inch-diameter post hole about 21 inches deep. The yield is printed on every bag; premium and fast-setting mixes match these numbers closely.
Should I add gravel or sand to bagged concrete mix?
No. Bagged concrete mix already contains cement, sand and gravel in the right ratio; just add water. Adding extra aggregate weakens it. (Bagged mortar and sand mix are different products with no gravel; don't substitute them for concrete.)
How much water per bag?
Roughly 3 quarts for an 80 lb bag and 2.25 quarts for a 60 lb bag, per the bag instructions. Use the minimum water that gives a workable, peanut-butter consistency. Soupier mixes finish easier but cure noticeably weaker.