Concrete Calculator
Calculate the exact amount of concrete needed for any slab project. Enter length, width, and depth in feet to get cubic yards, bags of premix, and total material cost with charts.
About This Calculator
The Concrete Calculator helps homeowners, contractors, and DIY builders estimate the exact volume of concrete required for slabs, driveways, patios, walkways, and other flatwork projects. Instead of guessing how many bags to buy or risking a costly shortfall, simply enter your slab's length, width, and depth to get instant, accurate results.
The calculator uses the standard volume formula: Volume (cubic feet) = Length × Width × Depth. It then converts cubic feet to cubic yards (divide by 27) and estimates the number of standard 60 lb premix concrete bags needed based on the industry-standard yield of 0.45 cubic feet per bag. The total material cost is calculated using average regional bag prices, which you can adjust.
Regional Notes
India: Concrete is commonly sold in ready-mix trucks by cubic meter. 1 cubic meter equals 1.308 cubic yards. Premix concrete bags are available in 20 kg and 40 kg sizes. Typical slab depth for residential projects is 100-150 mm (4-6 inches). Bag prices range from ₹300-₹400 for a 20 kg bag.
United States: Concrete is sold by cubic yard for ready-mix or in 60 lb / 80 lb bags for DIY projects. A 60 lb bag yields approximately 0.45 cubic feet. Standard driveway depth is 6 inches (0.5 ft). Bag prices average $5-$7 per 60 lb bag depending on region and brand.
United Kingdom: Ready-mix concrete is ordered by cubic meter. Premix bags are typically 25 kg, yielding about 0.4 cubic feet per bag. Common slab depths are 100-150 mm for domestic projects. Bag prices range from £5-£8 per 25 kg bag.
Always add 5-10% extra to your calculated volume to account for spillage, uneven ground, and measurement tolerances. For large projects, ready-mix concrete delivery is more economical than individual bags.
Frequently Asked Questions
How do I use this concrete calculator?
Enter the length, width, and depth of your slab in feet, then click Calculate. The tool instantly computes cubic yards, cubic feet, number of premix concrete bags needed, and total material cost.
How many bags of concrete do I need per cubic yard?
For a standard 60 lb bag yielding 0.45 cubic feet, you need about 60 bags per cubic yard (27 cu ft / 0.45 cu ft per bag). For 80 lb bags yielding 0.60 cubic feet, you need about 45 bags per cubic yard.
How much does a yard of concrete weigh?
One cubic yard of concrete weighs approximately 4,000 pounds or 1,814 kg. This varies slightly with the concrete mix and aggregate density used.
What is the formula for calculating concrete volume?
Concrete volume in cubic feet is calculated as Length (ft) × Width (ft) × Depth (ft). To convert to cubic yards, divide the total cubic feet by 27, since one cubic yard equals 27 cubic feet.
How long does concrete take to dry?
Concrete typically sets within 2-3 hours and achieves about 70% of its final strength within 7 days. Full curing to reach 99% compressive strength takes approximately 28 days under normal conditions.
What depth should a concrete slab be?
A standard concrete slab for patios and walkways is 4 inches (0.33 ft) deep. Driveways typically require 6 inches (0.5 ft), while heavy-duty applications like garage floors may need 8-10 inches (0.67-0.83 ft) of concrete.
How much does a concrete slab cost?
The cost of a concrete slab varies by region. In the US, expect $4-$8 per square foot for materials and labor for a standard 4-inch slab. In India, costs range from ₹50-₹80 per square foot. In the UK, prices range from £50-£80 per square meter.
Should I add a waste factor when ordering concrete?
Yes, experienced contractors typically add 5-10% extra concrete to account for spillage, uneven subgrades, and slight variations in form dimensions. Ordering 5-10% more than the calculated volume ensures you don't run short.