Concrete Calculator – Slabs, Bags, Footings, Posts & Cost
Concrete Calculator
Calculate concrete for slabs, bases, patios, paths, footings, trenches, circular areas, post holes, steps and multi-section jobs. Estimate ready-mix, bags, site-mix materials, labour and customer price.
Project & Measurement Units
Choose how you want to measure the job and what you are pouring.
Project Dimensions
Enter the dimensions for the selected project type.
Round Post Dimensions
Square / Rectangular Post Dimensions
Wastage / Over-Order Allowance
Add your own allowance for spills, uneven excavation, variation or measurement error.
How Are You Getting the Concrete?
Choose ready-mix, pre-mixed bags or an on-site mix estimate.
Ready-Mix Concrete
Pre-Mixed Concrete Bags
On-Site Mix Material Estimator
Labour & Other Job Costs
Optional contractor/job-pricing inputs. Leave anything you do not need at 0.
Additional Materials & Job Costs
Examples: reinforcement mesh, rebar, hardcore, sub-base, membrane, formwork, disposal, finishing materials or plant hire.Contractor Pricing
Optional selling-price calculation for tradespeople and contractors.
Your detailed quantity, bag, cost and pricing results will appear below.
Your Concrete Calculation
See your concrete quantity, wastage, purchasing requirement, material costs and estimated customer price.
Concrete Quantity
Your project dimensions converted into usable concrete volumes.
Concrete Purchasing
Quantity to purchase based on your selected supply method.
Estimated Site-Mix Materials
Based on the material quantities you entered per m³ or cubic yard.
Job Cost & Customer Price
Material, labour, markup and VAT / sales tax breakdown.
| Total Job Cost | £0.00 |
| Markup | £0.00 |
| Price Before Tax | £0.00 |
| VAT / Sales Tax | £0.00 |
| Final Estimated Customer Price | £0.00 |
Save Your Calculation
Generate a clean results sheet without the rest of the webpage.
This calculator provides quantity and cost estimates from the measurements and values entered by the user. Confirm dimensions, site conditions, supplier requirements and any structural specifications before ordering concrete or carrying out work.
Turn Your Concrete Estimate Into a Professional Quote
You've worked out the concrete quantity and job cost. Now turn those figures into a professional customer quote or invoice with the Handyman Hub Quote & Invoice Generator.
Pay once and use it whenever you need to create customer quotes and invoices.
How Much Concrete Do I Need?
Working out how much concrete you need is more than simply multiplying length by width. The shape of the project, concrete thickness, number of sections, post sizes, wastage allowance and the way you intend to buy the concrete can all affect the final quantity.
The Handyman Hub Concrete Calculator is designed for practical projects including concrete slabs, shed bases, garage bases, patios, paths, footings, foundations, trenches, post holes, circular pads and solid concrete steps.
It can also act as a concrete bag calculator, cubic yard concrete calculator and concrete cost calculator, allowing homeowners and contractors to estimate both the material requirement and the likely cost of the job.
How the Concrete Volume Calculation Works
Concrete volume is calculated from the physical dimensions of the area being filled. For a basic rectangular slab, the calculation is:
The important part is making sure all dimensions are converted into compatible units. This calculator does that automatically, so you can enter values such as a 5 metre length, 3 metre width and 100 millimetre slab thickness without manually converting 100 mm into 0.1 m.
Example: 5 m × 3 m Concrete Slab
A slab measuring 5 m long, 3 m wide and 100 mm thick requires:
5 × 3 × 0.1 = 1.50 m³ of concrete.
If a 10% wastage allowance is added, the total becomes:
1.50 × 1.10 = 1.65 m³.
Concrete Calculations for Different Project Types
Concrete Slabs & Bases
Calculate slabs, shed bases, garage bases, patios, paths, floors and other rectangular areas using length, width and thickness.
Footings & Foundations
Enter the footing length, width and depth to estimate concrete for strip footings, foundations and similar structural pours.
Concrete Trenches
Calculate concrete required to fill a trench using its total length, trench width and concrete depth.
Circular Concrete Areas
Circular slabs and pads use the diameter and depth. The calculator automatically works from the radius and circular area.
Post Holes
Estimate concrete for multiple cylindrical post holes and optionally subtract the space occupied by round or rectangular posts.
Concrete Steps
Estimate the volume of solid concrete steps using step width, tread depth, rise and the total number of equal steps.
Should You Add Extra Concrete for Wastage?
The exact calculated volume is the theoretical amount required to fill the dimensions entered. Real sites are rarely perfectly uniform, so some users choose to order slightly more concrete than the exact calculation.
Extra concrete may be useful where excavation is uneven, measurements are approximate, ground conditions vary or some material may be lost during placing.
The calculator does not force a particular wastage percentage. You can enter your own allowance or leave it at 0%.
Concrete Bag Calculator – How Many Bags Do I Need?
Bagged concrete is often used for smaller slabs, fence posts, repairs, paths and DIY projects. The number of bags required depends on the amount of finished concrete produced by each bag.
Bag weight alone is not enough to accurately calculate the quantity because different concrete products can produce different finished yields.
Use the yield shown on the manufacturer's packaging or product information. The calculator then converts the yield into the same volume units as the concrete project.
Why Whole Bags Must Round Up
Imagine a project needs 1.32 m³ of concrete and each bag produces 0.035 m³.
1.32 ÷ 0.035 = 37.71 bags.
You cannot buy 0.71 of a bag, so you would need 38 whole bags.
Those 38 bags would produce approximately 1.33 m³, leaving roughly 0.01 m³ surplus.
Metric, Cubic Feet and Cubic Yard Concrete Calculations
Concrete quantities are expressed differently around the world. Metric projects commonly use cubic metres, while concrete in the United States is frequently ordered in cubic yards.
| Measurement | Common Use | Approximate Conversion |
|---|---|---|
| Cubic metre (m³) | Metric ready-mix concrete | 1 m³ ≈ 1.308 yd³ |
| Cubic yard (yd³) | Common US ready-mix unit | 1 yd³ = 27 ft³ |
| Cubic foot (ft³) | Bag yield and smaller quantities | 1 m³ ≈ 35.315 ft³ |
| Litre | Small quantities and bag yield | 1,000 litres = 1 m³ |
The calculator performs the conversion automatically and shows the main concrete result in multiple volume units.
Ready-Mix Concrete vs Bagged Concrete
Ready-Mix Concrete
Ready-mix concrete is delivered to site and is often practical for larger pours where mixing many individual bags would take considerable time.
- Enter cost per cubic metre or cubic yard
- Add supplier delivery charges
- Add concrete pump costs where required
- Allow for supplier minimum charges
Pre-Mixed Concrete Bags
Bagged concrete can be convenient for smaller jobs, post holes and projects where access for ready-mix delivery is difficult.
- Enter the manufacturer's yield per bag
- Calculator always rounds up to whole bags
- See the actual purchased concrete volume
- Estimate unused surplus after rounding
Using the Calculator as a Concrete Job Estimator
Contractors, landscapers, builders and property maintenance businesses often need more than the quantity of concrete. The calculator can also estimate the total cost of completing the job.
Optional pricing inputs include concrete material cost, delivery, pump hire, equipment, labour and additional job expenses such as reinforcement, formwork, sub-base materials or waste disposal.
A markup can then be added to the job cost before any applicable VAT or sales tax is calculated.
Final customer price = Selling price + VAT / Sales Tax
The tax field is user-selectable rather than fixed to a particular country, making the estimator suitable for users in different regions.
Common Concrete Calculation Mistakes
- Entering slab thickness in metres when the measurement was actually taken in millimetres.
- Forgetting to include separate sections of a path, patio or foundation.
- Rounding the number of concrete bags down rather than up.
- Assuming every bag of the same weight produces the same amount of finished concrete.
- Forgetting that uneven excavation can increase the actual concrete requirement.
- Confusing cubic feet with cubic yards when ordering concrete.
- Forgetting delivery, pump, equipment or labour when estimating the total job cost.
- Confusing markup with profit margin when pricing a customer job.
Related Free Handyman Hub Calculators
Once you know the quantity and cost of the concrete, these calculators can help with the next stage of pricing your work.
Concrete Calculator FAQs
How do I calculate how much concrete I need?
For a rectangular area, multiply the length by the width by the concrete depth. Make sure the measurements are converted to compatible units before multiplying them. The calculator performs these conversions automatically.
How do I calculate concrete for a slab?
Measure the slab length, width and intended thickness. The concrete volume is length × width × thickness. For example, a 5 m × 3 m slab at 100 mm thick requires 1.5 m³ before any wastage allowance is added.
How many bags of concrete do I need?
Divide the total required concrete volume by the finished concrete yield from one bag. Always round the result up to the next whole bag. The yield should be taken from the manufacturer's product information because it can vary between products.
Does the calculator round concrete bags up?
Yes. The bag calculation always rounds upward to a whole bag. If the calculation produces 37.01 bags, the result will be 38 bags rather than 37.
How much concrete is in a cubic yard?
One cubic yard contains 27 cubic feet. One cubic metre is approximately 1.308 cubic yards. The calculator displays cubic metre, cubic foot and cubic yard results automatically.
How do I calculate concrete for post holes?
A round post hole is treated as a cylinder. Enter its diameter, depth and the number of holes. You can also choose to subtract the volume occupied by the post itself for a more detailed estimate.
Can I calculate multiple concrete areas together?
Yes. Choose the multiple sections option and add each rectangular section separately. You can also give each section a name so the results show the individual volume and overall total.
How much extra concrete should I order?
There is no single wastage percentage that is right for every project. Extra concrete may be required for uneven excavation, spills or measurement variation. The calculator lets you enter your own allowance rather than assuming a fixed percentage.
Can this calculator estimate the cost of concrete?
Yes. You can enter ready-mix cost per cubic metre or cubic yard, bag price, delivery, equipment, pump, labour and other costs. Contractors can also add markup and VAT or sales tax to estimate a final customer price.
Can I use the calculator for concrete footings and foundations?
Yes. The footing and trench modes calculate concrete volume from the dimensions you enter. The calculator estimates material quantity only and does not decide what structural footing dimensions are required.
Does the calculator work in both metric and imperial units?
Yes. Metric users can work with metres, centimetres and millimetres, while imperial users can enter feet and inches. Results also include cubic metres, cubic feet and cubic yards.
Is this calculator suitable for structural concrete design?
No. It is a quantity and cost estimator. Structural dimensions, reinforcement, concrete strength and mix specifications should follow the appropriate plans, engineer's design, building requirements or other applicable specification.