How Much Concrete Do You Actually Need?
Most of us have lived the pour-day nightmare at least once. The truck is empty, the finishers are waiting, and there is still a strip of form at the far end with nothing in it. A second short load costs more than the extra yard you should have ordered in the first place, and the cold joint never looks quite right.
This concrete calculator is built to stop that from happening. Pick the shape that matches your pour, type in the dimensions, and it gives you cubic yards, cubic feet, cubic meters, the approximate weight, and the bag count if you are mixing it yourself. Every result already includes the waste allowance you choose below.
Concrete Calculators
Slabs, Square Footings, or Walls
Driveways, patios, garage floors, sidewalks, rectangular footings, and poured walls.
Hole, Column, or Round Footing
Sonotube piers, deck footings, fence and post holes, and round columns.
Circular Slab or Tube
Round pads, ring footings, tank bases, and hollow columns or pipe surrounds.
Curb and Gutter Barrier
Combination curb and gutter runs for parking lots, subdivision streets, and site work.
Stairs
Poured concrete steps with a top landing, for porches, entries, and site stairs.
Block (CMU) Wall
How many concrete blocks a wall needs, with door and window openings taken out.
Block Fill (Grout)
Concrete or grout to fill the cores of a block wall, fully or partially grouted.
Sand, Gravel, & Stone
Base course, bedding sand, drainage gravel, and crushed stone in cubic yards and tons.
Brick Wall
Face brick and veneer walls, with bricks, mortar bags and openings taken out.
Mortar
Bags of mortar mix for a brick or block job, from the number of units you are laying.
Rebar for a Slab
Rebar grid for slabs on grade and mats: bar count, linear feet, 20 ft sticks and weight.
Post Hole Concrete
Fence posts, deck posts and mailboxes, with the post itself taken out of the hole volume.
Pavers, Base & Sand
Patios, walkways and driveways: paver count, gravel base and bedding sand.
Retaining Wall Block
Segmental retaining walls: blocks, caps, base gravel and drainage stone.
Concrete Cost
Rough material cost for a pour, using your local ready-mix price and fees.
Mortar bag counts use a common rule of thumb of about 36 bricks or 11 blocks (8 x 16 in) per 80 lb bag of mortar mix; joint size and technique change this. Rebar totals do not include laps, chairs, or dowels beyond the waste allowance. Retaining wall results assume a 24 x 6 in gravel base and 12 in of drainage stone; follow the block maker’s design guide. Block counts use the nominal face size including the mortar joint. Grout volumes are typical core volumes for standard two-core units. Aggregate weights are dry, loose averages; confirm with your supplier. Concrete weights assume normal-weight concrete at about 150 lb per cubic foot (roughly 4,050 lb per cubic yard). Bag counts use typical yields of 0.30 cu ft for a 40 lb bag, 0.45 cu ft for a 60 lb bag and 0.60 cu ft for an 80 lb bag; check the yield printed on the brand you buy.
These calculators give quantity and weight estimates for planning only. They are not a quote, a bid, or an engineered design.
Prices for concrete, block, grout and aggregate are not the same in every state. Material costs, delivery and short-load fees, sales tax, and labor rates change from state to state, city to city, and even between suppliers in the same town, and they move with the market. Local codes, mix designs, and product sizes can also differ by region.
Always confirm quantities, specifications, and current pricing with your local supplier, engineer, or building department before you order. For project-specific numbers priced to your city and county, request an estimate from our team.
Using the Concrete Calculator Step by Step
The math behind concrete is simple. The mistakes come from measuring in a hurry, mixing units, and forgetting the parts of the pour that are not flat. Here is the routine we follow when we check a quantity, whether it is a backyard patio or a commercial slab on grade.
- Measure the formed area, not the drawing. Plans are a starting point, but forms move. Pull a tape inside the forms before you order.
- Pick the right shape. A thickened slab edge is really a slab plus a strip footing. Run each part in its own row and add them up.
- Keep units honest. Thickness is almost always in inches and length in feet. Each input has its own unit menu, so you do not have to convert anything by hand.
- Set your waste allowance. We use 10% on most residential work. Go higher on uneven subgrade, and lower on tight, laser-graded commercial pours.
- Round up to what you can actually buy. Ready-mix plants batch in quarter or half-yard steps, and nobody sells half a bag.
A Real Example: A 20 by 12 Foot Patio
A homeowner outside Austin wants a 20 x 12 ft patio at 4 inches thick. That is 240 sq ft x 0.333 ft = 80 cubic feet, or 2.96 cubic yards. Add 10% for waste and the subgrade dips and you are at about 3.26 yards, so you order 3.5.
Mixing it by hand would take around 147 bags of 80 lb concrete. That is several pallets, a mixer, and a crew that will be very tired by lunch. For anything over about a yard, ready-mix almost always wins on labor alone.
Ready-Mix or Bagged Concrete?
For setting a few fence posts or pouring a small pad for an AC unit, bags make sense. You control the timing and there is no minimum order. Once you cross roughly one cubic yard, the trip to the supply yard and the hours of mixing start to cost more than a truck.
Keep in mind that many suppliers charge a short-load fee on small orders, so a 2-yard pour can cost almost as much as 4. Ask the plant about it when you call, along with the slump and the mix strength your inspector or engineer wants.
How Many Bags of Concrete Are in a Yard?
- 80 lb bags: about 45 per cubic yard
- 60 lb bags: about 60 per cubic yard
- 40 lb bags: about 90 per cubic yard
The calculator does this conversion for you and rounds each count up to whole bags.
Common Mistakes That Leave You Short on Pour Day
- Trusting the nominal thickness. A “4-inch” slab poured over a soft, rutted base often averages 4.5 inches or more. That half inch adds up to over 12% more concrete.
- Forgetting the footings. Thickened edges, interior beams under a monolithic slab, and pier caps all hold concrete. Run them separately.
- Skipping the pump line. If you are pumping, the line holds concrete that never reaches the forms. Ask your pump operator how much to add.
- Mixing up diameter and radius. The round calculators ask for diameter. Put in the radius and you will order a quarter of what you need.
- No plan for leftovers. A little extra is cheap insurance. Have a small form or a few splash blocks ready so it does not go to waste.
How Each Concrete Volume Is Calculated
Every input is converted to feet first, then the volume is worked out in cubic feet and divided by 27 to get cubic yards.
- Slab, footing, or wall: length x width x thickness x quantity
- Round column or hole: 3.1416 x (diameter / 2)² x depth x quantity
- Circular slab or tube: 3.1416 / 4 x (outer diameter² – inner diameter²) x height x quantity
- Curb and gutter: [curb depth x (curb height + flag thickness) + gutter width x flag thickness] x length x quantity
- Block wall: (wall length x wall height – openings) / face area of one block (0.889 sq ft for an 8 x 16 in block)
- Block fill: number of blocks x core volume per block x share of cores filled (about 0.27 cu ft per 8 in block)
- Sand, gravel, and stone: length x width x depth / 27 = cubic yards, then x weight per cubic yard / 2,000 = tons
- Brick wall: net wall area x 144 / [(brick length + joint) x (brick height + joint)]; a modular brick with a 3/8 in joint is about 6.9 bricks per sq ft
- Rebar grid: bars each way = (slab dimension – 2 x cover) / spacing + 1, times bar length, times weight per foot
- Post holes: (hole area – post area) x depth x number of posts
- Pavers: area x 144 / paver face area, plus base depth and sand bed depth x area / 27 for cubic yards
- Retaining wall: courses (exposed height / block height + buried courses) x blocks per course (length / block length)
- Stairs: each step adds run x (rise x step number) x width, and the top platform adds platform depth x (rise x number of risers) x width
Block Walls, Grout, and Base Rock
Block is counted by face area, not volume. A standard 8 x 16 in block covers about 0.89 sq ft of wall, so you need roughly 113 blocks for every 100 sq ft. Take doors and windows out first, then add waste for cuts and broken units at the corners.
Grout is where block jobs quietly run over. A solid-grouted 8 in wall takes about 1 cubic yard for every 100 blocks. Most reinforced walls are only grouted at the rebar cells, so pick the share of cores your structural drawings actually call for.
Sand, gravel, and stone are sold by the ton, but your plans give you area and depth. The calculator converts one to the other with a typical weight per cubic yard. Moisture and gradation change that weight, so confirm it with the quarry when the number is tight.
When a Calculator Is Not Enough
A concrete calculator is perfect for a driveway, a slab, or a set of steps. On a commercial job it is only the first pass. Those projects carry grade beams, drilled piers, elevated decks, equipment pads, and rebar that all have to be taken off from the structural set under CSI Division 03.
That is the work our estimators do every day. Our concrete and masonry takeoff services give you quantities by pour, element, and drawing sheet, prepared and checked by human estimators. If you want to see the format first, open our concrete work sample.
Concrete Calculator Questions
Quick answers to what contractors and homeowners ask most before ordering concrete.
How much concrete do I need for a 10 x 10 slab?
At 4 inches thick, a 10 x 10 ft slab needs about 33.3 cubic feet, or 1.23 cubic yards. With 10% waste, plan on about 1.36 cubic yards. That works out to roughly 62 bags of 80 lb concrete.
How many 80 lb bags of concrete make a cubic yard?
About 45. An 80 lb bag yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet. Always check the yield printed on the bag, since it varies a little by brand.
How much extra concrete should I order?
Most crews add 5% to 10%. Go toward 10% or more on uneven or hand-graded subgrade, deep footings, or when pumping. Running out mid-pour costs far more than a small amount left over.
How much does a cubic yard of concrete weigh?
Normal-weight concrete weighs about 4,000 to 4,050 lb per cubic yard, or roughly 145 to 150 lb per cubic foot. Lightweight mixes weigh noticeably less.
Can I use this calculator for a commercial bid?
It is a good check for simple elements. For a full bid, you need a takeoff from the structural drawings that covers footings, grade beams, slabs, walls, and rebar. Our estimators prepare those by hand, usually within 24 to 48 hours.
Get a Complete Concrete Takeoff in 24–48 Hours
Send us your plans and bid date. Our estimators will take off every footing, slab, wall, and pier, and send back quantities you can price with confidence.