--- title: "How Much Concrete Do You Need for a Patio Slab?" site: ProCalc.ai type: Blog Post category: how-to domain: Construction url: https://procalc.ai/blog/concrete-patio-slab-calculator markdown_url: https://procalc.ai/blog/concrete-patio-slab-calculator.md date_published: 2026-03-10 date_modified: 2026-03-27 read_time: 7 min tags: concrete, patio, slab, how-to, concrete calculator, cubic yards --- # How Much Concrete Do You Need for a Patio Slab? **Site:** [ProCalc.ai](https://procalc.ai) โ€” Free Professional Calculators **Category:** how-to **Published:** 2026-03-10 **Read time:** 7 min **URL:** https://procalc.ai/blog/concrete-patio-slab-calculator > *This file is served for AI systems and search crawlers. Human page: https://procalc.ai/blog/concrete-patio-slab-calculator* ## Overview Calculate exactly how much concrete you need for a patio slab so you don't run short mid-pour or waste money over-ordering. ## Article I Messed This Up Once and It Wasn't Fun I was helping a buddy pour a patio behind his garage โ€” maybe five years ago now โ€” and we eyeballed the concrete order. Just kind of guessed. We figured "eh, it's a small slab, we'll get a yard and a half and that should be plenty." We ran out with about a third of the slab still bare, and by the time we got more bags from the hardware store and mixed them by hand in a wheelbarrow, the first section had already started setting up on us. The finished result looked.. not great. Like two different patios that happened to be touching each other. So yeah, measure your concrete. Actually measure it. The good news is the math isn't hard. It's honestly one of the simpler calculations you'll do on any project, and once you get the hang of it, you'll never waste money over-ordering (or worse, under-ordering) again. The Actual Math Behind a Patio Slab Concrete is sold by the cubic yard in most of North America, or by the cubic meter in other places. Either way, you need to figure out the volume of your slab โ€” length times width times depth. That's it. But people trip up on the unit conversions, which is where things get messy. ๐Ÿ’ก THE FORMULA Volume = Length ร— Width ร— Thickness Length = the long dimension of your slab (in feet or meters) Width = the short dimension (in feet or meters) Thickness = how deep the slab is โ€” typically 4 inches for a patio To convert cubic feet โ†’ cubic yards: divide by 27 To convert cubic inches โ†’ cubic feet: divide by 1,728 Let me walk through a real example because the formula alone doesn't always click. Say you're pouring a patio that's 12 feet by 16 feet, and you're going 4 inches thick (which is pretty standard for a residential patio โ€” you don't need 6 inches unless you're parking something heavy on it). First, convert that 4 inches to feet: 4 รท 12 = 0.333 feet. Then multiply: 12 ร— 16 ร— 0.333 = 63.94 cubic feet. Now divide by 27 to get cubic yards: 63.94 รท 27 = 2.37 cubic yards . Most people round up to about 2.5 yards to account for spillage, uneven ground, and the fact that forms are never perfectly straight no matter how careful you are. I always tell people to add roughly 10% as a buffer โ€” concrete is one of those things where having a little extra is way better than coming up short. If you don't want to do any of this by hand, I built a concrete calculator that handles the conversions for you. Common Patio Sizes and How Much Concrete They Need I put together this table because I kept getting asked the same questions over and over. These assume a 4-inch thick slab with the 10% waste factor already baked in. Patio Size (ft) Thickness Cubic Yards Needed Approx. 80-lb Bags 8 ร— 10 4 inches 1.1 about 90 10 ร— 12 4 inches 1.6 about 134 12 ร— 16 4 inches 2.6 about 217 14 ร— 20 4 inches 3.8 about 317 16 ร— 24 4 inches 5.3 about 440 20 ร— 20 4 inches 5.4 about 450 Look at that last row. 450 bags! That's why anything bigger than about 2 cubic yards, most people call a ready-mix truck. Mixing 200+ bags by hand is genuinely brutal โ€” I've done it, and my back still reminds me about it on cold mornings. A typical ready-mix truck can carry around 8 to 10 cubic yards, and there's usually a minimum order of about 1 yard (though some companies charge a short-load fee if you order under 3 or 4 yards). It's worth calling around. If you're also figuring out the cost side of things, our concrete cost estimator can help you ballpark the total spend including delivery. Stuff That Throws Off Your Numbers The formula is simple but the ground isn't. Here's what I mean โ€” your yard probably isn't perfectly level. If one corner of your excavation is half an inch deeper than the other side (and it will be, unless you're incredibly meticulous with a laser level), that extra volume adds up across a 200-square-foot slab. This is exactly why the 10% buffer matters. Other things that eat concrete: Gravel sub-base that's uneven โ€” the concrete fills in the low spots between stones Forms that bow outward slightly under the weight of wet concrete Spillage around the edges, which is basically unavoidable Any slope you're building into the slab for drainage (you want about 1/8 inch per foot away from the house, by the way) I've seen people calculate perfectly and still come up a quarter yard short because the ground underneath just wasn't as flat as they thought. If you're pouring on undisturbed soil and you compacted your gravel base well, you'll be closer to the calculated number. But if the ground was recently backfilled or you're working with clay that shifts around, pad that estimate a bit more โ€” maybe 15% instead of 10. And one more thing that trips people up: if you're adding a thickened edge (sometimes called a turned-down edge or a monolithic footing) around the perimeter, that's extra volume you need to account for. A thickened edge might go down 8 or 12 inches instead of 4, and it runs the entire perimeter of the slab. Use our volume calculator to figure out that extra section separately, then add it to your main slab volume. For the reinforcement side of things โ€” whether you're using rebar or wire mesh โ€” check out our rebar calculator and our area calculator to figure out coverage. And if you're doing any grading work before the pour, the gravel calculator is handy for sizing your sub-base, and our cubic yard calculator works for basically any bulk material. Quick Tips From Pouring Way Too Many Patios Order your concrete for morning delivery if you can. Afternoon pours in the summer are miserable because the heat makes the concrete set faster than you can work it, and you end up with a rough finish that's hard to fix. Have at least two people. Honestly, three is better. Wet the gravel base before the truck arrives โ€” dry gravel sucks moisture out of the concrete and can cause weak spots at the bottom of the slab. You don't want standing water, just damp. And make sure your forms are staked solidly every 3 to 4 feet, because wet concrete is heavy (a 4-inch slab weighs roughly 50 pounds per square foot) and it will push your forms out if they're not braced properly. I've seen beautiful straight forms turn into wobbly curves the second the chute starts pouring. For finishing, a square footage calculator helps if you're figuring out how much sealer or stamping release agent you need after the pour. How many bags of concrete do I need for a 10ร—10 patio? For a 10ร—10 slab at 4 inches thick, you need about 1.23 cubic yards of concrete. That works out to roughly 100 bags of 80-lb premix (each bag yields about 0.6 cubic feet). Honestly, at that quantity, you're right on the edge of where a ready-mix truck starts making more sense โ€” especially if you factor in the labor of mixing all those bags. Is 4 inches thick enough for a patio? Yes โ€” 4 inches is standard for foot traffic, patio furniture, grills, all the normal stuff. Go to 6 inches if you're supporting something heavier, like a hot tub or a vehicle. How much extra concrete should I order beyond my calculation? Add 10% as a general rule. If your subgrade is rough or you're working with forms that aren't perfectly rigid, bump it to 15%. Running short mid-pour is one of the worst things that can happen on a concrete job โ€” you can't just pause and come back tomorrow. --- ## Reference - **Blog post:** https://procalc.ai/blog/concrete-patio-slab-calculator - **This markdown file:** https://procalc.ai/blog/concrete-patio-slab-calculator.md ### AI & Developer Resources - **LLM index:** https://procalc.ai/llms.txt - **LLM index (full):** https://procalc.ai/llms-full.txt - **MCP server:** https://procalc.ai/api/mcp - **Developer docs:** https://procalc.ai/developers ### How to Cite > ProCalc.ai. "How Much Concrete Do You Need for a Patio Slab?." ProCalc.ai, 2026-03-10. https://procalc.ai/blog/concrete-patio-slab-calculator ### License Content ยฉ ProCalc.ai. Free to reference and cite. Do not republish in full without attribution.