Figure poured-concrete volume, bags and cost for the shape you’re actually pouring — slab, footing, round or square column, wall, steps or curb — add several pours, then read the total in cubic yards and cubic metres, for every bag size at once.
Units
ShapeDimensionsQtyVolume
5–10% is typical for spillage and uneven subgrade.
Volume and bag math only — mix design, reinforcement and finishing are up to you. Bag yields are the standard 40/50/60/80 lb product yields; cost fields are editable examples, not a quote. Suppliers differ on minimums, short-load fees and rounding, so treat this as an order estimate.
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Pouring more than just concrete?
Filling block cores? Get the wall block count first with the Concrete Block Calculator, then bring the core-fill volume back here. Need a compacted sub-base under the slab? The Gravel Calculator gives it in tons and yards, and the Board Foot Calculator totals the lumber for your forms.
What this concrete calculator does — and its lane
This is a poured-concrete volume tool: it turns the dimensions of what you’re pouring into cubic yards, cubic feet and cubic metres, then into bags and cost. It is built for figuring concrete yardage across the shapes a real job actually contains — not just a rectangular slab. If instead you’re counting concrete or cinder blocks for a wall, that’s a different job: use the concrete block calculator for the block count and come back here only for the core-fill volume.
The shapes: slab, footing, column, wall, steps, curb
Most concrete estimators only do a slab, so a footing or a row of round-column piers means doing the math twice by hand. Here you pick a shape per pour and stack them into one total.
Slab / floor / pad — length × width × thickness. The everyday patio, garage floor or driveway pour.
Footing — length × width × depth, times how many footings. Long strip or a run of pads.
Round column / tube form — π × radius² × height, times the count. The radius is half the tube diameter.
Square column / post — side × side × height, times the count.
Wall / stem wall — length × height × thickness.
Steps / stairs — the solid concrete in a flight, figured as a stepped triangular prism: each step adds rise, so the cross-section is roughly (steps × rise × run) ÷ 2, times the width. Enter run, rise, width and the number of steps.
Once the volume is known, the calculator divides by the standard bag yields to count bags — and shows all four sizes, not just one, so you can compare trips and price. It also costs the job two ways: by the ready-mix yard and by the bag, because the cheaper option flips depending on size.
Bag
Yield (ft³)
Bags per yd³
40 lb
0.30
90
50 lb
0.375
72
60 lb
0.45
60
80 lb
0.60
45
These are the common Quikrete and Sakrete product yields and are facts of the bag, not a brand price table. As a public 2026 ballpark, ready-mix runs roughly $125–$175 per cubic yard delivered and an 80 lb bag is around $6 — enter your own local numbers in the price fields, which are fully editable.
Slab thickness, screed and metric
Slab thickness drives the whole estimate: a 4″ slab and a 6″ slab of the same footprint differ by half again in volume and cost, so set it deliberately. UK readers often call the finished concrete surface the screed and order by the cubic metre — the calculator shows m³ alongside cubic yards so you can hand a metric figure to the supplier and a yardage figure to anyone working in imperial without converting anything yourself.
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Frequently asked questions
How do I calculate how much concrete I need?
Find the volume of each pour, then add them up. Slab or footing: length′ × width′ × (thickness″ ÷ 12). Round column or tube form: π × radius² × height. Sum the pours, divide by 27 for cubic yards, and add 5–10% waste. This tool does it live and also gives bags and cost.
How many bags of concrete are in a cubic yard?
A cubic yard is 27 ft³. Divided by each bag’s yield that’s about 90 × 40 lb, 72 × 50 lb, 60 × 60 lb or 45 × 80 lb bags. Bag math gets expensive fast, so most people move to ready-mix once a project passes about one cubic yard.
How much concrete for a 10x10 slab?
100 ft². At 4″ that’s about 33.3 ft³ = 1.23 yd³ before waste (~56 bags of 80 lb, or ~62 with 10% waste); at 6″ it’s 50 ft³ = 1.85 yd³. Enter your own numbers above for the exact figure.
Bags or ready-mix — which is cheaper?
Bags usually win under about one cubic yard, where ready-mix adds short-load fees. Above one to two yards ready-mix is cheaper and far less work. The calculator costs both ways — ready-mix uses the per-yard field, bags use the per-bag field. As a 2026 example, ready-mix is roughly $125–$175/yd³ and an 80 lb bag about $6; use your local prices.
How much waste should I add?
5–10% is standard, for spillage, uneven subgrade, varying slab thickness and the bit left in the chute. Use the low end for a tidy slab on a level base and the high end for footings on rough ground. Running short mid-pour costs far more than a small overage, so round up.
What’s the volume of a round-column form?
π × radius² × height, with radius = half the tube diameter. A 12″ tube 4′ tall holds ~3.14 ft³; four of them ~12.6 ft³, just under half a yard. Pick the round-column shape, enter diameter and height, and set the count.