Concrete Bag Calculator

How many bags of concrete do you need? Enter slab, post hole, or volume dimensions for instant bag counts, weight, water, and cost — imperial or metric.

Enter a length greater than 0.

Enter a width greater than 0.

Enter a thickness greater than 0.

Typical: 10% for most pours. Common thickness: patios 4 in, driveways 4-6 in.

Select a size to apply a price and highlight that row.

Applies to the selected bag size only.

Concrete Bag Calculator: Bags, Weight & Coverage Guide

This calculator estimates how many bags of concrete you need for slabs, post holes, footings, and pads, in either imperial or metric units. Enter dimensions on the slab or post hole tab, or enter a known volume directly. Results show bag counts, total weight, estimated water, and optional material cost. Works for standard bagged concrete mixes, including Quikrete, Sakrete, and most other pre-mixed bag brands, since yields are similar across manufacturers.

How many bags of concrete per cubic yard? (imperial)

Bag sizeYield per bagBags per cubic yardWeight per yardTypical price/bag (2026)
40 lb0.30 ft³90 bags3,600 lb$4–$6
50 lb0.375 ft³72 bags3,600 lb$5–$7
60 lb0.45 ft³60 bags3,600 lb$5–$8
80 lb0.60 ft³45 bags3,600 lb$6–$10

Yields vary slightly by product and mix design — check your bag label. 60 and 80 lb bags highlighted as most common for DIY projects. See Data Sources.

How many bags of concrete per cubic metre? (metric)

Bag sizeYield per bagBags per m³Weight per m³
20 kg9.4 L (0.0094 m³)~107 bags~2,136 kg
25 kg11.7 L (0.0117 m³)~85 bags~2,136 kg
40 kg18.7 L (0.0187 m³)~53 bags~2,136 kg

Based on a typical bagged mix density of ~2,136 kg/m³. Confirm with your product's packaging, since density varies by brand.

How many square feet does a bag of concrete cover?

Coverage depends on slab thickness: the thicker the pour, the fewer square feet each bag covers. Divide a bag's yield (in cubic feet) by your thickness in feet to get coverage. Use the table below for the three most common slab depths.

Bag sizeCoverage at 2 inCoverage at 4 inCoverage at 6 in
40 lb1.8 sq ft0.9 sq ft0.6 sq ft
50 lb2.25 sq ft1.13 sq ft0.75 sq ft
60 lb2.7 sq ft1.35 sq ft0.9 sq ft
80 lb3.6 sq ft1.8 sq ft1.2 sq ft

Example: for a 4 in thick walkway, an 80 lb bag covers about 1.8 sq ft — so 100 sq ft needs roughly 56 bags before waste. 2 in is typical for thin toppings/patches, 4 in for patios and walkways, 6 in for driveways.

Concrete bags by project size

ProjectVolume80 lb bags60 lb bagsReady-mix?
Fence post (12" dia × 36" deep)2.4 ft³ / 0.09 yd³4 bags6 bagsNo (use bags)
10×10 ft patio, 4 in thick33.3 ft³ / 1.23 yd³62 bags74 bagsBorderline
12×12 ft patio, 4 in thick48 ft³ / 1.78 yd³88 bags107 bagsConsider ready-mix
20×20 ft driveway, 4 in thick133 ft³ / 4.94 yd³246 bags296 bagsYes (order ready-mix)
10×20 ft garage floor, 6 in thick100 ft³ / 3.70 yd³185 bags222 bagsYes (order ready-mix)

Includes 10% waste. Ready-mix typically becomes cost-effective over 1.5-2 cubic yards depending on local delivery minimums.

Bags vs ready-mix

For most DIY projects under 1 cubic yard, including fence posts, small pads, footings, bagged concrete is the practical choice. No minimum order, no delivery scheduling, and you can mix at your own pace. For pours over 1.5-2 cubic yards, the maths shift: a cubic yard requires 45 bags of 80 lb concrete, each needing to be mixed separately. At that volume, ready-mix saves significant labour time and often costs less once you factor in bags, rental mixer, and your time.

Frequently Asked Questions

Divide your total cubic feet by the yield per bag, then round up. An 80 lb bag yields 0.60 ft³. For a 10×10 ft slab at 4 inches thick: 10 × 10 × (4÷12) = 33.3 ft³ ÷ 0.60 = 56 bags. Add 10% waste = 62 bags. The calculator above handles this instantly.
Exactly 45 bags of 80 lb concrete per cubic yard (27 ft³ ÷ 0.60 ft³/bag). For 60 lb bags: 60 per yard. For 50 lb bags: 72 per yard. For 40 lb bags: 90 per yard.
It depends on thickness. An 80 lb bag (0.60 ft³) covers about 3.6 sq ft at 2 in, 1.8 sq ft at 4 in, or 1.2 sq ft at 6 in thick. A 60 lb bag covers roughly 2.7, 1.35, and 0.9 sq ft at those same depths. To calculate: divide the bag's yield in cubic feet by your thickness in feet.
A 50 lb bag of concrete yields about 0.375 cubic feet once mixed. That works out to 72 bags per cubic yard (27 ft³ ÷ 0.375 ft³).
A 60 lb bag of concrete yields about 0.45 cubic feet once mixed. That works out to 60 bags per cubic yard (27 ft³ ÷ 0.45 ft³).
Bagged concrete mix is sold by its dry weight: 40 lb, 50 lb, 60 lb, and 80 lb bags are the standard US sizes. In metric markets, 20 kg, 25 kg, and 40 kg bags are most common. The 60 lb/80 lb (or 20 kg/25 kg) sizes are most common for DIY slabs, footings, and posts.
A 10×10 ft slab at 4 inches thick = 33.3 ft³ = 1.23 cubic yards. With 10% waste: approximately 62 bags of 80 lb or 74 bags of 60 lb. At this size, consider ordering ready-mix to avoid mixing 60+ bags by hand.
A standard 12-inch hole at 36 inches deep = 2.36 ft³. At 0.60 ft³ per 80 lb bag: 4 bags per hole (rounded up with waste). Use the Post Holes tab above for a total across all holes.
For pours over 1.5-2 cubic yards, ready-mix is usually faster and often cheaper. A yard of concrete = 45 bags of 80 lb. Mixing by hand takes several hours. Ready-mix minimums are typically 1 yard with a delivery fee.
Most 80 lb bags require 3-4 quarts (0.75-1 gallon, ~3.3 litres) of water. 60 lb bags need about 3 quarts (~2.8 litres). Always follow the manufacturer's label — adding too much water is the most common DIY mistake and significantly weakens the finished concrete. See Data Sources.
Use 10% for most pours. Use 5% for simple rectangular slabs with clean formwork. Use 15% for complex shapes or multiple small pours. It's always better to have one extra bag than run short mid-pour.
Yes. Switch Unit system to Metric at the top of the calculator to enter dimensions in metres and centimetres, and get results in 20 kg, 25 kg, or 40 kg bag counts, kilograms, tonnes, and litres of water.

Concrete Bag Planning Checklist

Reviewed by Maria Ramirez, PE. Covers site prep, formwork, reinforcement, ordering, mixing procedure, and curing steps.

Download Checklist (PDF)

Planning reference only. See Methodology and Data Sources. View all project checklists →

Accuracy & Review

Reviewed by: Maria Ramirez, PE

Maria is a licensed Professional Engineer with experience in residential and light commercial concrete quantity takeoffs. She reviewed the formulas, unit conversions, rounding rules, and default yield assumptions used in this calculator.

Last updated:

See: Methodology · Data Sources · Review Board

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Disclaimer: Results are for general planning only and do not constitute engineering or structural design advice. Actual quantities vary based on site conditions, slab thickness, reinforcement, and local code requirements.

See Methodology and Data Sources for details.