Concrete Calculator
Calculate concrete volume for slabs, footings, columns and round tubes in cubic yards and cubic metres, then convert it to 40, 60 or 80 lb bags or truck loads.
Bags of pre-mixed concrete
Approximate wet weight: 5,500 lb / 2,492 kg (about 150 lb per ft³ / 2,400 kg per m³).
Rectangular volume = length × width × depth; round pours use π r² h. Cubic yards = cubic feet ÷ 27. A 10% waste allowance is included above. Bag yields follow the standard printed figures (0.30 / 0.45 / 0.60 ft³) — check your own bag, and order ready-mix by the truck to your supplier's minimum. Estimates only, not a substitute for a contractor's take-off.
What is the Concrete Calculator?
The ByteTools Concrete Calculator works out how much concrete a pour needs. Choose a shape — a rectangular slab, footing or wall, a round column or tube, a square pier, or a circular pad — enter the dimensions, and it returns the volume in cubic yards, cubic metres and cubic feet with a waste allowance included.
- Slabs, footings, walls, round tubes, square piers and circular pads
- Results in cubic yards, cubic metres and cubic feet at once
- Bag counts for 40 / 60 / 80 lb and 20 / 25 / 30 kg bags
- Ready-mix truck loads and approximate wet weight
- Adjustable waste allowance, 10% by default
- Imperial and metric, calculated entirely in your browser
How to use the Concrete Calculator
- 1
Choose imperial or metric, then pick the shape you are pouring.
- 2
Enter the dimensions — length, width and depth for a slab, or diameter and height for a column or tube.
- 3
Set how many identical pours you need and the waste allowance (10% by default).
- 4
Read the volume in cubic yards and cubic metres, and the bag count for the bag size you plan to buy.
About the Concrete Calculator
The ByteTools Concrete Calculator works out how much concrete a pour needs. Choose a shape — a rectangular slab, footing or wall, a round column or tube, a square pier, or a circular pad — enter the dimensions, and it returns the volume in cubic yards, cubic metres and cubic feet with a waste allowance included.
It then converts that volume into something you can actually buy: the number of 40, 60 or 80 lb bags, or 20, 25 and 30 kg bags in metric, plus how many ready-mix truck loads it represents and the approximate wet weight. Multiple identical pours can be counted in one go.
All arithmetic happens in your browser and nothing is uploaded. Bag yields differ slightly between manufacturers and site conditions vary, so use the result to plan and order rather than as a substitute for a contractor's take-off. If you are near the crossover between bagging it yourself and ordering ready-mix, price both — hand-mixing much more than a cubic yard is a very long day.
Frequently asked questions
How do I calculate cubic yards of concrete?
Multiply length by width by depth with every dimension in feet, then divide by 27 because a cubic yard is 27 cubic feet. A 10 ft by 10 ft slab at 4 inches thick is 10 × 10 × 0.333 = 33.3 cubic feet, which is 1.23 cubic yards before any waste allowance.
How many 80 lb bags of concrete are in a cubic yard?
An 80 lb bag of pre-mixed concrete yields about 0.60 cubic feet, so a cubic yard takes 45 bags. The same maths gives 60 bags of 60 lb and 90 bags of 40 lb. Above roughly one cubic yard, ready-mix is usually cheaper and far less work.
How much concrete do I need for a fence post?
A typical 10-inch-wide hole 24 inches deep holds around 0.9 cubic feet of concrete once the post itself is deducted, which is one and a half 80 lb bags. Most posts land between one and two bags — our fence calculator works this out for a whole run at once.
How much extra concrete should I order?
A 10% waste allowance is the usual site figure, and this calculator applies it by default. It covers spillage, an uneven subgrade and slight over-excavation. Running short mid-pour creates a cold joint, so erring high is much cheaper than erring low.
How much does a cubic yard of concrete weigh?
Wet concrete weighs roughly 150 lb per cubic foot, so a cubic yard is about 4,050 lb — a little over two US tons. In metric that is around 2,400 kg per cubic metre. The calculator shows the weight so you can check what your trailer or barrow run can handle.
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