How many 80 lb bags of concrete make a cubic yard?

You need 45 bags of 80 lb concrete to make one cubic yard. Since 1 cubic yard equals 27 cubic feet and each 80 lb bag yields 0.6 cubic feet, the calculation is: 27 ÷ 0.6 = 45 bags.

How many 40 kg bags of concrete make a cubic metre?

You need 50 bags of 40 kg concrete to make one cubic metre. Since each 40 kg bag yields approximately 20 litres (0.020 cubic metres), the calculation is: 1,000 litres ÷ 20 = 50 bags.

How much area does an 80 lb bag of concrete cover?

An 80 lb bag covers approximately 1.8 square feet at 4 inches thick (or 0.17 square metres at 10 cm thick). The coverage increases with thinner applications: at 2 inches thick (5 cm), one 80 lb bag covers about 3.5 square feet. For metric: a 40 kg bag covers about 0.20 square metres at 10 cm thick. Calculate coverage by dividing the bag's yield by your desired thickness.

How do I calculate how many concrete bags I need?

Calculate volume: Multiply length × width × thickness (in feet or metres) Divide by bag yield: Use 0.6 cubic feet for 80 lb bags or 0.020 cubic metres for 40 kg bags Add 10-15% extra to account for waste and spillage

How many bags of concrete do I need for a 10×10 slab?

For a 10×10 slab at standard 4-inch thickness, you need 55 bags of 80 lb concrete (imperial) or 45 bags of 40 kg concrete (metric). This is based on a volume of 33 cubic feet (0.9 cubic metres). Always add 10% extra for a total of about 60-61 bags (imperial) or 50 bags (metric).

Do I need the same amount of cement as concrete?

No. Cement is just one ingredient in concrete. Concrete is a mixture of cement, sand, gravel, and water. The bagged concrete you buy already contains all these ingredients pre-mixed in the correct proportions. You're buying complete concrete mix, not just cement.

Can I mix different bag sizes?

Yes, you can mix different bag sizes, but it's best to buy primarily one size for easier calculation and consistent mixing. You can use smaller bags to top off your project. Just ensure you mix each bag with the correct water ratio according to the manufacturer's instructions.

What if I run short on concrete?

Running short creates cold joints - weak spots where old and new concrete meet. These joints compromise structural integrity and appearance. Always order 10-15% extra material to avoid this problem. It's better to have leftover concrete than to create a weak point in your project.

Should I use bagged concrete or ready-mix?

Bagged concrete: Best for projects under 1-2 cubic yards / 0.75-1.5 cubic metres (small patios, fence posts, repairs) Ready-mix: More economical and easier for projects over 2 cubic yards / 1.5 cubic metres (driveways, large slabs, garage floors) Consider ready-mix when you need more than 60-70 bags, as it saves labour and ensures consistency

How long does bagged concrete last?

Unopened bags last 3-6 months if stored properly in a dry location off the ground. After this period, the cement can begin to hydrate from moisture in the air and lose strength. Store bags on pallets in a covered area for maximum shelf life.

How to Estimate Concrete Bags: Complete Calculator Guide

Name: Chippy Tools
Rating: 3.890 (119 reviews)
Author: Chippy Tools

Wondering how many bags of concrete you need for your patio, driveway, or fence posts? Getting this calculation wrong can cost you time and money. This comprehensive guide shows you exactly how to estimate concrete bags accurately, whether you’re working in imperial or metric units.

Quick Reference: Concrete Bag Yields

Before diving into calculations, here’s what you need to know about common bag sizes:

Imperial (US) Bags:

40 lb bag = 0.30 cubic feet
60 lb bag = 0.45 cubic feet
80 lb bag = 0.60 cubic feet

Metric Bags:

20 kg bag = 0.010 cubic metres
25 kg bag = 0.0125 cubic metres
40 kg bag = 0.020 cubic metres

Understanding Concrete Volume Measurements

Concrete volume is measured in cubic feet (ft³) or cubic yards (yd³) in the imperial system, and cubic metres (m³) in the metric system. Your first step is always calculating the total volume needed before determining bag quantities.

Key Conversion:

1 cubic yard = 27 cubic feet 1 cubic metre = 1,000 litres

Step-by-Step: Calculate Your Concrete Volume

For Slabs, Patios, and Driveways

Formula: Length × Width × Thickness = Volume

Imperial Example:

Length: 10 feet
Width: 10 feet
Thickness: 4 inches (convert to feet: 4 ÷ 12 = 0.33 feet)
Volume: 10 × 10 × 0.33 = 33 cubic feet

Metric Example:

Length: 3 metres
Width: 3 metres
Thickness: 10 cm (convert to metres: 0.10 metres)
Volume: 3 × 3 × 0.10 = 0.9 cubic metres

For Fence Posts and Footings

Formula: π × radius² × depth = Volume per hole

Imperial Example:

Post hole diameter: 8 inches (radius: 4 inches = 0.33 feet)
Depth: 2 feet
Volume per hole: 3.14 × 0.33² × 2 ≈ 0.68 cubic feet
For 10 posts: 0.68 × 10 = 6.8 cubic feet total

Metric Example:

Post hole diameter: 20 cm (radius: 10 cm = 0.10 metres)
Depth: 0.6 metres
Volume per hole: 3.14 × 0.10² × 0.6 ≈ 0.019 cubic metres
For 10 posts: 0.019 × 10 = 0.19 cubic metres total

Calculate Concrete Volume in Seconds

Download Chippy Tools for instant concrete volume calculations with support for slabs, footings, and cylinders in both imperial and metric units.

Converting Volume to Bag Quantities

Once you know your volume, calculating bags is simple division.

Formula: Total Volume ÷ Bag Yield = Number of Bags

Example: 10×10 Slab (4 inches thick)

Imperial Calculation:

Volume needed: 33 cubic feet
Using 80 lb bags: 33 ÷ 0.60 = 55 bags
Using 60 lb bags: 33 ÷ 0.45 = 74 bags
Using 40 lb bags: 33 ÷ 0.30 = 110 bags

Metric Calculation:

Volume needed: 0.9 cubic metres
Using 40 kg bags: 0.9 ÷ 0.020 = 45 bags
Using 25 kg bags: 0.9 ÷ 0.0125 = 72 bags
Using 20 kg bags: 0.9 ÷ 0.010 = 90 bags

Common Project Calculations

How many 80 lb bags make a cubic yard?

1 cubic yard = 27 cubic feet

27 ÷ 0.6 = 45 bags of 80 lb concrete

How many 40 kg bags make a cubic metre?

1 cubic metre = 1,000 litres

Since a 40 kg bag yields 20 litres:

1,000 ÷ 20 = 50 bags of 40 kg concrete

4×4 Slab (4 inches thick)

Imperial: 4 × 4 × 0.33 = 5.28 cubic feet

Bags (80 lb): 5.28 ÷ 0.6 = 9 bags

Metric: 1.2 × 1.2 × 0.10 = 0.144 cubic metres

Bags (40 kg): 0.144 ÷ 0.020 = 8 bags

10×10 Slab (4 inches thick)

Imperial: 10 × 10 × 0.33 = 33 cubic feet

Bags (80 lb): 55 bags

Metric: 3 × 3 × 0.10 = 0.9 cubic metres

Bags (40 kg): 45 bags

20×20 Slab (4 inches thick)

Imperial: 20 × 20 × 0.33 = 132 cubic feet

Bags (80 lb): 220 bags

Metric: 6 × 6 × 0.10 = 3.6 cubic metres

Bags (40 kg): 180 bags

Stop Guessing, Start Calculating

Get accurate concrete volumes for any project size. Chippy Tools provides professional-grade calculations that help you order the right amount every time.

Coverage Area Per Bag

How much area does an 80 lb bag cover?

At 4 inches (0.33 ft) thick:

0.6 ÷ 0.33 = 1.8 square feet per bag

At 2 inches (0.17 ft) thick:

0.6 ÷ 0.17 = 3.5 square feet per bag

How much area does a 40 kg bag cover?

At 10 cm (0.10 m) thick:

0.020 ÷ 0.10 = 0.20 square metres per bag

At 5 cm (0.05 m) thick:

0.020 ÷ 0.05 = 0.40 square metres per bag

Pro Tips for Accurate Estimates

Always Add Extra Material

Add 10-15% extra to your calculated amount to account for:

Spillage and waste
Uneven subgrade
Form irregularities
Measurement errors

Example: If you need 50 bags, order 55-58 bags.

Consider Your Project Size

Small projects (under 1 cubic yard / 1 cubic metre): Use bagged concrete for convenience and control.

Large projects (over 2 cubic yards / 2 cubic metres): Consider ready-mix concrete delivery. It’s often more economical and ensures consistent quality for:

Driveways
Garage floors
Large patios
Pool decks

Thickness Matters

Standard concrete thickness by project type:

Sidewalks: 4 inches (10 cm)
Patios: 4 inches (10 cm)
Driveways: 4-6 inches (10-15 cm)
Garage floors: 6 inches (15 cm)
Fence posts: 6-12 inches diameter (15-30 cm)

Chippy Tools: Your Concrete Volume Calculator

The Chippy Tools concrete volume calculator eliminates manual calculation errors:

Select your project type (slab, footing, or cylinder)
Input your dimensions in imperial or metric units
Get instant, accurate volume calculations
Use the volume to determine your bag quantities with the formulas above

The calculator provides precise cubic measurements in both cubic feet/yards and cubic metres, helping you avoid costly overages or project delays from underestimating.

Ready to Eliminate Concrete Calculation Errors?

Download Chippy Tools and access professional concrete calculators with built-in safety margins for accurate material estimates every time.

Cost Estimation Guide

Typical Price Ranges:

Bagged concrete prices vary by location and retailer:

40 lb / 20 kg bags: Lower price range per bag
60 lb / 25 kg bags: Mid-range price per bag
80 lb / 40 kg bags: Higher price per bag (but better value per cubic foot/metre)
Ready-mix concrete: Priced per cubic yard/metre with minimum order and delivery fees

Cost Comparison Considerations:

For a typical 10×10 slab (requiring about 55 bags of 80 lb concrete or 45 bags of 40 kg concrete or 1.2 cubic yards / 0.9 cubic metres):

Bagged concrete: Total cost includes bags only, but requires significant labour for mixing
Ready-mix: Higher upfront cost per project, but includes delivery and professional mixing

General Rule: For projects requiring more than 1-2 cubic yards / 0.75-1.5 cubic metres, ready-mix typically becomes more cost-effective when factoring in labour time and consistency.

Site Preparation Checklist

Before ordering concrete:

Excavate to proper depth
Install forms securely
Add 4-6 inches (10-15 cm) of compacted gravel base
Ensure proper drainage slope
Have mixing tools ready (if using bags)
Check weather forecast (avoid freezing temps)
Arrange helpers (concrete sets quickly)

When to Call a Professional

Consider hiring professionals if:

Your project exceeds 2 cubic yards (1.5 cubic metres)
You need reinforced concrete
Local codes require permits and inspections
You lack proper mixing equipment
The project requires precise finishing

Final Takeaway

Accurate concrete estimation comes down to three simple steps:

Calculate volume (length × width × thickness)
Divide by bag yield (based on your bag size)
Add 10-15% extra for waste

The Chippy Tools concrete volume calculator takes the guesswork out of step one, providing instant, accurate volume calculations for slabs, footings, and cylindrical holes. Whether you’re setting fence posts or pouring a new patio, proper planning with professional tools prevents costly mistakes and ensures perfect results.

Start Your Project With Confidence

Join thousands of professionals and DIYers who trust Chippy Tools for accurate concrete calculations. Download now and never over-order or run short again.