Concrete Calculator
With length 12 ft, width 12 ft, thickness 4 inch, waste allowance 10 percent and 1 more field, concrete comes to 1.96 cu yd — concrete needed. It is reached in 8 steps, the last of which is 52.8 / 27, and each one is printed on the page with its numbers filled in. The formula is the one published by American Concrete Institute, not an approximation fitted to it.
Cubic yards of concrete for a slab, round pad, footing, column, wall or stairs, with bag counts and cost.
Formula and sources checked · How we check
Pour type Slab — rectangular, Length 12 ft, Width 12 ft, Thickness 4 inch
1.96 cu yd
Concrete needed for the inputs in this link. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- Volume
48 cu ft- Volume with waste
48 * (1 + 10 / 100)52.8 cu ft- Concrete needed
52.8 / 271.956 cu yd- Cubic meters
1.9555556 * 0.76455491.495 m3- 60 lb bags (0.45 cu ft each)
ceil(52.8 / 0.45)118 bags- 80 lb bags (0.60 cu ft each)
ceil(52.8 / 0.6)88 bags- Weight of the pour
1.9555556 * 40507,920 lbs- Ready-mix cost at that price
1.9555556 * 145283.556
Several at once
A job is rarely one of anything. Work out the first, add it, change the figures and add the next — the list keeps what each line was, and totals them.
Ask about this in the chatCompare: 4-inch slab against 6-inchConcrete for a 10 × 10 Slab by Thickness
Worked example
A 10×10 patio at 4 in thick is 33.3 cu ft, or 1.36 cu yd with 10% waste — 82 sixty-pound bags, or about $197 of ready-mix. Past roughly 1 cu yd, delivery is usually cheaper than bags and always faster.
How to work it out yourself
- 1.Measure length and width in feet, and thickness in inches. For a footing, measure the trench; for a column, measure the hole.
- 2.Divide the thickness by 12 to put it in feet, then multiply all three dimensions together for cubic feet.
- 3.Divide cubic feet by 27 to get cubic yards, which is the unit every supplier quotes in.
- 4.Add 5–10% for waste. Subgrade is never flat and running short mid-pour creates a cold joint.
- 5.Under about a cubic yard, divide cubic feet by 0.45 for 60 lb bags or 0.60 for 80 lb bags. Above it, order ready-mix.
How far one cubic yard goes
A cubic yard is 27 cubic feet. Spread one inch deep it covers 324 square feet, and every other depth is that figure divided by the depth in inches — which is the whole table in one sentence.
| Depth | Square feet | Square yards |
|---|---|---|
| 1 in | 324 | 36.0 |
| 2 in | 162 | 18.0 |
| 3 in | 108 | 12.0 |
| 4 in | 81 | 9.0 |
| 6 in | 54 | 6.0 |
| 8 in | 41 | 4.5 |
| 10 in | 32 | 3.6 |
| 12 in | 27 | 3.0 |
Cubic yards for a given area
| Area | 1 in | 2 in | 3 in | 4 in | 6 in | 8 in | 10 in | 12 in |
|---|---|---|---|---|---|---|---|---|
| 100 sq ft | 0.31 | 0.62 | 0.93 | 1.23 | 1.85 | 2.47 | 3.09 | 3.70 |
| 200 sq ft | 0.62 | 1.23 | 1.85 | 2.47 | 3.70 | 4.94 | 6.17 | 7.41 |
| 500 sq ft | 1.54 | 3.09 | 4.63 | 6.17 | 9.26 | 12.35 | 15.43 | 18.52 |
| 1,000 sq ft | 3.09 | 6.17 | 9.26 | 12.35 | 18.52 | 24.69 | 30.86 | 37.04 |
Suppliers deliver in whole or half yards, so round up — a truck will not bring 2.37.
Bags to the cubic yard
| Bag | Holds | Bags per yard |
|---|---|---|
| Mulch, 2 cu ft bag | 2 cu ft | 14 |
| Mulch, 3 cu ft bag | 3 cu ft | 9 |
| Topsoil or compost, 1 cu ft bag | 1 cu ft | 27 |
| Concrete mix, 80 lb bag | 0.6 cu ft | 45 |
| Concrete mix, 60 lb bag | 0.45 cu ft | 60 |
| Concrete mix, 40 lb bag | 0.3 cu ft | 90 |
Concrete is sold by weight and the yield is printed on the bag, which is why it takes 45 of the 80 lb bags to make a yard rather than the dozen people expect. Past about ten bags, ready-mix is cheaper and far less work.
Depth by use
| Use | Depth | Why |
|---|---|---|
| Mulch, established beds | 2–3 in | Deeper than 3 in holds water against stems and starves roots of air. |
| Mulch, new beds over bare soil | 3–4 in | The extra inch is what suppresses weeds for a season. |
| Topsoil over an existing lawn | 0.25–0.5 in | Any more and the grass underneath is smothered rather than fed. |
| Topsoil for a new lawn | 4–6 in | Roots need the depth once, at the start; it cannot be added later. |
| Gravel walkway | 2–4 in | Over a compacted base, not over soil. |
| Gravel driveway, surface course | 3–4 in | Over 6 to 8 in of compacted base. |
| Gravel driveway, full build | 8–12 in | Base and surface together, laid and compacted in layers. |
| Concrete patio or walkway | 4 in | Four inches is the ordinary residential slab. Follow the specification for anything carrying a vehicle. |
How much extra to order
| Reason | Add | Note |
|---|---|---|
| Compaction, crushed stone | 20% | Six inches loose settles to about five. Order for the finished depth. |
| Settling, mulch and soil | 10–15% | Organic material shrinks as it breaks down over the first season. |
| Spillage and uneven ground | 5–10% | A hole is never the rectangle it was measured as. |
| Concrete, sub-base variation | 5–10% | A slab poured half an inch deep over 200 sq ft is a third of a yard nobody ordered. |
Concrete for a 10 × 10 slab by thickness
| Thickness (inch) | Concrete needed | 60 lb bags (0.45 cu ft each) | 80 lb bags (0.60 cu ft each) |
|---|---|---|---|
| 2 | 0.68 cu yd | 41 bags | 31 bags |
| 3 | 1.02 cu yd | 62 bags | 46 bags |
| 4 | 1.36 cu yd | 82 bags | 62 bags |
| 5 | 1.70 cu yd | 102 bags | 77 bags |
| 6 | 2.04 cu yd | 123 bags | 92 bags |
| 8 | 2.72 cu yd | 163 bags | 123 bags |
| 10 | 3.40 cu yd | 204 bags | 153 bags |
| 12 | 4.07 cu yd | 245 bags | 184 bags |
Volumes include the default 10% waste allowance. Thickness drives volume linearly — 6 in costs half again as much as 4 in.
What does it cost?
Typical price is $125–$165 per cu yd. Delivered ready-mix, before any short-load fee. Suppliers commonly add $50–150 for loads under about 3 cubic yards.
| Item | Typical price |
|---|---|
| Ready-mix, delivered | $125–$165 per cu yd |
| Pre-mix, 50 lb bag | $4–$8 per bag |
| Pre-mix, 60 lb bag | $5–$9 per bag |
| Pre-mix, 80 lb bag | $6–$11 per bag |
Price ranges as of 2026. Materials pricing moves — treat these as a sanity check on a quote, not as a quote.
The formula
- Volume
- Volume with waste
48 * (1 + 10 / 100) - Concrete needed
52.8 / 27 - Cubic meters
1.9555556 * 0.7645549 - 60 lb bags (0.45 cu ft each)
ceil(52.8 / 0.45) - 80 lb bags (0.60 cu ft each)
ceil(52.8 / 0.6) - Weight of the pour
1.9555556 * 4050 - Ready-mix cost at that price
1.9555556 * 145
Source: American Concrete Institute, Portland Cement Association
Questions people actually ask
- At what point should I order ready-mix instead of bags?
- Around 1 cubic yard. That is 60 sixty-pound bags, about 1.8 tons to haul and mix by hand, and most suppliers set their short-load minimum near that same volume.
- Why does the calculator add waste?
- An excavated subgrade is never perfectly flat, so real placements run 5–10% over the geometric volume. Running short mid-pour creates a cold joint, which is a structural defect, not a cosmetic one.
- How thick should the slab be?
- 4 in for patios and walkways, 5–6 in for driveways carrying passenger vehicles, 6 in or more with reinforcement for anything carrying trucks. Thickness drives volume linearly, so 6 in costs 50% more concrete than 4 in.
- How is the volume of stairs calculated?
- Each step is a slab sitting on the ones below it, so the solid is a staircase of slabs: width × rise × run × n(n+1)/2. Four 7.5 in by 11 in steps at 4 ft wide come to 22.9 cu ft (0.85 cu yd) — five-eighths of the enclosing box. The fraction is (n+1)/2n, so it only approaches half on a long flight.
- How much does a cubic yard of concrete weigh?
- About 4,050 lb, or just over two tons. That is why a full truck carries around 8 cubic yards and why a wheelbarrow moves roughly 0.1 of a yard at a time.
- What is the difference between cement and concrete?
- Cement is one ingredient of concrete, not a synonym for it. Concrete is cement, sand, coarse aggregate and water; the cement is only about 10 to 15% of the mix by volume and is what binds the rest. Mortar is cement and sand with no coarse aggregate, which is why it goes between bricks and not under them. The truck on site is a concrete truck whatever the sign says.
- How long does concrete take to cure?
- It does not dry, it reacts — cement and water bond chemically, which is why concrete sets underwater. In normal conditions you can walk on it after 24 to 48 hours, drive a car on it after 7 days, and it reaches about 70% of its design strength in those 7 days. Full design strength is quoted at 28 days, which is the age test cylinders are broken at. Keeping it damp for the first week matters more than the weather after it.
- What is concrete mixed from, and in what ratio?
- A common general-purpose mix is 1 part cement to 2 parts sand to 3 parts coarse aggregate by volume, with enough water to bring the water-to-cement ratio to about 0.5 by weight. More water makes it easier to place and weaker once set, which is the trade nobody mentions on site. Bagged mixes have the ratio already made up, so only the water is yours to get wrong.
Related
- Gravel & Aggregate CalculatorCubic yards and tons of gravel, sand, limestone or topsoil for an area at a given depth.
- Square Footage CalculatorSquare footage of a room, wall, border, gable end, ring or triangle from feet-and-inches measurements, with a waste factor and the cost.
- Brick CalculatorBricks and mortar for a wall, by brick size — modular, queen, king or utility. Includes the mortar bags and the masonry sand, at about 125 bricks a bag.
- Board Foot CalculatorConvert lumber dimensions to board feet and price out a cut list, including nominal-vs-actual sizing.
- Fence CalculatorPosts, rails, pickets and concrete for a run of fence at a given post spacing. Sections, posts, rails, pickets and the two bags of concrete each post takes.
- Cubic Yard CalculatorCubic yards for any footprint and depth, with a waste allowance and the weight of the debris if you are hauling it away.
Part of a job
- Building a deck — 7 pages, in the order the questions arrive
- Pouring concrete — 6 pages, in the order the questions arrive
Worked out already
The same calculator with the numbers filled in. Each one computes on the server, so the answer is in the page rather than waiting on a click.
Read first
- What a Concrete Patio Costs — Materials, delivery and labour for a slab, and where the price actually moves: on a small pour the concrete is rarely the largest of the three figures.
- What a Deck Costs to Build — Decking, framing and fasteners priced out, and why the board decides the total: the framing under it barely changes between a cheap deck and a costly one.
- What a Fence Costs — Post spacing, the ground-contact rating most people buy wrong, and why corners and gates cost more per foot than the long straight runs between them.
Put this calculator on your site
Free, no attribution required beyond the link.
<iframe src="https://rulecalculators.com/embed/concrete" width="100%" height="420" style="border:1px solid #e7e4de;border-radius:12px" title="Concrete Calculator"></iframe>Straight to your case
The control above covers every case. These are the same calculator fixed to one of them, with the formula for that case written out.
- Concrete Slab CalculatorYards and Bags
- Concrete Footing CalculatorTrench Volume
- Sonotube and Column CalculatorPost Holes
- Concrete Stairs CalculatorPer Flight
- Concrete Wall CalculatorYards per Wall