Calculate how much concrete you need in cubic yards and bags for slabs, driveways, sidewalks, and fence posts.
LotSite starting assumption
LotSite starting assumption
LotSite starting assumption
The prices filled in here are LotSite starting assumptions, not quotes and not sourced prices. Prices differ by region and supplier, so type in a local quote and the estimate will use it.
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Cubic yards and 80-lb bags needed for a 4-inch slab.
Dollar figures here use LotSite starting assumptions, not quotes and not sourced prices. Use the calculator above with a local quote for your own number.
| Area | Cu Yards | 80-lb Bags | Bag Cost | Ready-Mix |
|---|---|---|---|---|
| 50 sq ft | 0.6 | 28 | $196 | $93 |
| 100 sq ft | 1.2 | 56 | $392 | $185 |
| 200 sq ft | 2.5 | 112 | $784 | $370 |
| 400 sq ft | 4.9 | 223 | $1,561 | $741 |
| 600 sq ft | 7.4 | 334 | $2,338 | $1,111 |
| 1,000 sq ft | 12.3 | 556 | $3,892 | $1,852 |
The most important step in any concrete project is accurate measurement. Ordering too little means a cold joint (where fresh concrete meets hardened concrete), which creates a structural weakness. Ordering too much wastes money. Add 5 to 10 percent to your calculated volume for waste and spillage.
For small projects (under 1 cubic yard), bagged concrete mix is practical. Just add water and mix in a wheelbarrow or mixer. For anything larger, order ready-mix delivery. Most ready-mix companies have a minimum order of 1 cubic yard and charge short-load fees for small deliveries.
Use LotSite to measure your project area on satellite imagery. View your driveway, patio, or walkway area on satellite imagery and get the square footage, especially useful for irregularly shaped areas.
Volume is area times thickness, converted to cubic yards, with no waste added. The guide above says to add 5 to 10 percent, and the calculator leaves that to you so the base number stays comparable with a supplier's quote. Bag counts use the yields printed on standard bagged mix, 0.45 cubic feet from a 60-lb bag and 0.60 cubic feet from an 80-lb bag, rounded up to whole bags.
The thickness you pick is assumed everywhere. A real slab poured over a hand-raked gravel base averages more than its nominal depth, because the low spots fill first, and a 4-inch slab that averages 4.5 inches needs about 12 percent more concrete. Thickened edges, footings under a slab edge, and steps are extra volume on top of that. After the base is compacted, measure the depth to the top of the forms at several points and use the average, not the plan number.
Ready-mix at $150 per cubic yard assumes a full-price yard with no short-load fee. Plants set a minimum order and charge extra below it, so a single-yard pour can cost well above the per-yard rate; ask for the delivered price for your quantity. Bagged mix at $5.50 and $7.00 per bag is material only. Mixing more than about a yard by hand is a long day, so budget a rented mixer past that point, and have help on site, because concrete does not wait.
The fence post option assumes 1.5 bags of 60-lb mix per hole. Work out your own hole before you buy for all of them: a 10-inch hole 2 feet deep holds about 1.1 cubic feet, and after a 4x4 post takes its share about 0.9 cubic feet is left to fill, which is 2 bags of 60-lb mix or 1.5 bags of 80-lb. Bigger posts, wider auger-dug holes, and holes that caved in while digging take more.
Enter your address and measure the area for your concrete pour on satellite imagery.
Also check out our paver calculator and gravel calculator