Last checked
May 12, 2026
We checked the page logic, support notes, and related links on this page.
Concrete volume tool
Concrete Calculator
Estimate concrete volume and rough material cost for slabs, footings, and post holes.
Volume + tonnes + unitsWaste-aware resultBuying checks
How to use it
Planning before buying
Use this calculator for a planning check, then confirm the final order or quote against live product data and site conditions.
Why trust it
See how the site is maintained
Read the calculator methodology and editorial policy for the standards behind these pages.
Planning summary
Quick answer
Best for converting dimensions and depth into a delivered quantity before you choose bagged, bulk, or loose supply.
Planning summary
Watch most
The most common mistakes are mixing up depth units, forgetting overbreak, and ignoring uneven excavation.
Planning summary
Best next move
Measure carefully, sense-check the result against supplier pack sizes, and add a practical allowance for cuts, breakage, or site variation.
Recently used calculators
Pick up from the calculators you used recently on this device.
Quote-ready brief
Use these actions to turn the live calculator result into a cleaner request for builders, suppliers, or merchants.
Run the calculator, then use these actions to prepare the estimate for a real quote request.
Need help deciding what to ask for? Read the quote checklist or contact the team at hello@buildcostlab.com.
Practical checks before you buy
These notes are where BuildCostLab goes beyond a generic calculator result by surfacing the assumptions, buying traps, and next decisions that usually move the real order.
What this estimate includes
The measured volume, waste-adjusted buying quantity, density or unit-size conversion, and a rough material spend when a price is entered.
What it may not include
Unexpected excavation differences, compaction behaviour, haulage constraints, and local delivery charges unless you add them separately.
Key assumptions
Assumes simple shapes, typical ordering practice, and a clear volume estimate before ordering ready-mix or bagged concrete.
Worked example
Example: a 4m by 3m slab at 100mm depth gives 1.2m3 before waste. Add 10 percent and the planning quantity becomes 1.32m3, which is the number to compare against bagged or ready-mix buying routes.
How this estimate is worked out
We multiply length by width by depth, add the waste allowance, then convert the adjusted volume into tonnes or whole buying units using the stated density and delivery format.
What assumptions sit underneath it
Assumes simple shapes, typical ordering practice, and a clear volume estimate before ordering ready-mix or bagged concrete.
How rounding is handled
Because bulk materials are bought by bag, bulk bag, tonne, or loose load, the final answer rounds to a real buying quantity rather than stopping at the theoretical trench or base volume.
What changes the result most
Installed depth, loose-versus-compacted behaviour, density assumptions, and buying format usually move the real order fastest.
When this estimate breaks
Remeasure when excavation depth changes across the job, the substrate is uneven, or the supplier grades the material differently from your assumption.
Practical buying checks
Compare bags, bulk bags, loose loads, minimum order quantities, access for delivery vehicles, and whether the site can store the chosen route.
Quote-ready checklist
Use these prompts when you want to turn the estimate into a clearer builder, installer, or merchant request.
- State the measured area, target depth, and whether the depth is compacted or loose-delivered.
- Ask how the material will be supplied: bags, bulk bags, loose load, or ready-mix route where relevant.
- Flag any access, storage, delivery, or waste-removal limits before the first quote is treated as final.
Explore this project hub
Open the full Concrete Estimating project hub to move from quick estimate to deeper guidance.
Related calculators in the same project hub
Use these linked tools when the estimate crosses into another calculator in the Concrete Estimating cluster rather than stopping at one isolated material number.
Footing Concrete Calculator
Estimate footing concrete volume, order quantity, and rough cost for trench and strip foundations.
Slab Concrete Calculator
Estimate slab concrete volume, order quantity, and rough cost from slab dimensions and depth.
Quick answers
These answers are designed to resolve the last practical buying questions people usually have after running the calculator.
How much concrete do I need for a slab?
Multiply slab length by width by depth, then add a sensible contingency amount.
Should I round up a concrete order?
Yes. Most jobs need a small margin because running short is disruptive.
Use this estimate in a quote request
Copy the estimate, add your own notes, and send the same scope to each builder or supplier so the quotes are easier to compare.
- Confirm what the quote should include: materials only, labour only, or both.
- State access, finish level, timing, and any unknowns clearly.
- Ask each supplier or installer to price the same scope and exclusions.
You can also open the wider Concrete Estimating project hub if the quote depends on more than one material.