How much concrete do I need for a 10×10 slab?

At the standard 4-inch thickness: 10 × 10 × 0.333 = 33.3 ft³ = 1.23 yd³. With a 10% waste allowance, order 1.5 yd³ (ready-mix is sold in quarter-yard steps). Hand mixing instead? That's 56 bags of 80 lb mix.

How many 80 lb bags make a yard of concrete?

One 80 lb bag yields 0.60 ft³, and a cubic yard is 27 ft³ — so 27 ÷ 0.60 = 45 bags per yard. For 60 lb bags it's 60, and for 40 lb bags it's 90. Above roughly one yard, ready-mix is almost always cheaper and far less work.

Should I order concrete in cubic yards or cubic meters?

US and Canadian ready-mix plants sell by the cubic yard; most other countries sell by the cubic meter. This calculator reports both, so read whichever line matches your supplier. 1 yd³ = 0.765 m³.

What waste percentage should I use?

10% covers typical spillage, over-excavation and slab thickness variation. Drop to 5% only for formed pours on a compacted, laser-leveled base. Use 15% when pouring against bare earth (trench footings) or hand mixing, where batch-to-batch yield varies.

Does the calculator account for rebar displacing concrete?

No, and it shouldn't. Reinforcement typically occupies under 2% of the section, which is well inside the waste allowance. Estimators ignore steel displacement for quantity takeoffs.

How much does a yard of concrete weigh?

Normal-weight concrete runs about 4,050 lb (roughly 2 US tons) per cubic yard, or 2,400 kg/m³. That matters for delivery access — a fully loaded 10-yard mixer truck exceeds 66,000 lb and will crack a residential driveway it parks on.

Concrete

Concrete Calculator

Enter dimensions in any units — feet, inches, meters — and get the volume to order, bag counts and total weight. Built around the same takeoff method estimators use.

MaterialsCalc Editorial TeamConstruction Estimating EditorsJuly 15, 2026

Concrete Calculator

Volume, weight and bag count for any rectangular pour. Switch units freely — the math is handled for you.

How this calculator works

Four steps, the same ones a professional estimator follows on every takeoff.

The calculator multiplies length × width × depth to get a gross volume, converts every input to a common unit first (so mixing feet with inches is fine), multiplies by your pour count, then adds a waste allowance. The result is reported in cubic yards for US ready-mix orders and cubic meters for metric suppliers, alongside a bag count if you're mixing on site.

The concrete volume formula

Formula

V = L × W × D × N × (1 + waste)

V: volume to order (yd³ or m³)
L: length of the pour
W: width of the pour
D: depth or thickness
N: number of identical pours
waste: allowance as a decimal (0.10 = 10%)

All three dimensions must be in the same unit before multiplying. Divide cubic feet by 27 to get cubic yards; divide by 35.31 to get cubic meters.

The only part people get wrong is unit conversion. Thickness is usually quoted in inches while plan dimensions are in feet — 4 inches is 0.333 ft, not 0.4. Every formula on this site converts internally, but if you're checking by hand, do the conversion first, not last. The full method, including irregular shapes, is covered step by step in our guide to calculating concrete.

Worked examples

Worked example

A 24 × 24 ft two-car garage slab, poured 6 inches thick on a compacted gravel base.

1
Convert thickness to feet
6 in ÷ 12 = 0.5 ft
2
Gross volume
24 × 24 × 0.5 = 288 ft³
3
Convert to cubic yards
288 ÷ 27 = 10.67 yd³
4
Add 10% waste
10.67 × 1.10 = 11.73 yd³

Result: Order 12 yd³ of ready-mix (rounded to the quarter yard).

Metric example

A 6 m × 1.2 m garden path, 100 mm thick, mixed by hand from 80 lb bags.

1
Convert thickness to meters
100 mm = 0.10 m
2
Gross volume
6 × 1.2 × 0.10 = 0.72 m³
3
Add 15% waste for hand mixing
0.72 × 1.15 = 0.83 m³
4
Divide by the 80 lb bag yield (0.017 m³)
0.83 ÷ 0.017 = 48.8

Result: 49 bags of 80 lb concrete mix — at that count, price ready-mix too.

Common estimating mistakes

Running short mid-pour is the expensive failure: a cold joint forms in about 30–45 minutes in warm weather, and most plants charge a short-load fee of $50–100 for the rescue truck. The cheapest insurance is ordering the extra quarter yard. Current plant pricing and fee structures are broken down in the concrete cost guide.

Concrete weight quick reference

Weight drives truck access, pump decisions and structural loads. Full tables in the density chart.

Typical unit weights per PCA. See the complete concrete density chart for ingredients and special mixes.
Material	kg/m³	lb/ft³	t/m³
Normal-weight concrete (plain)PCC, unreinforced	2,300	143.6	2.3
Normal-weight concrete (reinforced)≈1–2% steel by volume	2,400	149.8	2.4
High-density / heavyweight concreteMagnetite or barite aggregate; radiation shielding	3,800	237.2	3.8
Structural lightweight concreteExpanded shale/clay aggregate, ASTM C330	1,750	109.2	1.75

Frequently asked questions

Concrete guides & references

How to Calculate ConcreteThe full method: measure, convert, add waste, order.Guide Concrete Cost GuideReady-mix, bagged and delivered prices with real math.Guide Concrete Density ChartUnit weights for every common concrete type.Chart Concrete Coverage GuideWhat a yard — or a bag — actually covers.Guide Concrete Mix Ratio GuideNominal mixes from 1:3:6 to 1:1:2, with yields.Guide Concrete Curing GuideStrength gain timeline and curing methods that work.Guide Concrete vs AsphaltCost, lifespan and maintenance compared honestly.Comparison

Need a shape-specific tool?

Concrete Slab Calculator Concrete Footing Calculator Concrete Wall Calculator Concrete Column Calculator

Paving with asphalt instead?

Sources & references

[1]ASTM C94/C94M: Standard Specification for Ready-Mixed Concrete — ASTM International, 2024
[2]ACI 318-19: Building Code Requirements for Structural Concrete — American Concrete Institute, 2019
[3]Design and Control of Concrete Mixtures, 17th ed. — Portland Cement Association, 2021