Last checked
May 12, 2026
We checked the page logic, support notes, and related links on this page.
Compacted base-layer tool
Sub-Base Calculator
Estimate sub-base volume, tonnes, and delivered quantity for paving, patios, paths, and driveway foundations before you order.
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 common misses are underestimating the depth needed for the build, ignoring soft spots or level corrections, and confusing loose-delivered tonnage with the compacted finished layer.
Planning summary
Best next move
Check the compacted target depth against the actual build-up first, because level corrections and weak formation can use more sub-base than the neat footprint suggests.
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
Sub-base estimates work best when the footprint, compacted layer depth, and the intended base specification are clear before the order is placed.
Worked example
Example: a 6m by 3m patio base at 120mm depth gives 2.16m3 before waste. Add 10 percent and the planning quantity becomes 2.376m3. At roughly 1.8 tonnes per m3, that is about 4.28 tonnes, so five 0.85-tonne bulk bags is the safer planning order.
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
Sub-base estimates work best when the footprint, compacted layer depth, and the intended base specification are clear before the order is placed.
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
Compacted depth, density, the final paved footprint, and any level correction in the formation usually move the sub-base order fastest.
Where people under-order
Base layers often rise above the paper total once weak spots, edge thickening, and level corrections are added back into the build-up.
Practical buying checks
Compare MOT Type 1, hardcore, and other graded routes, then check whether bulk bags or loose tonnes fit the site access and spreading plan best.
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 Aggregate and Base Estimating project hub to move from quick estimate to deeper guidance.
Related calculators for the same groundwork build-up
Use these linked tools when the base estimate also needs hardcore, membrane coverage, MOT Type 1, or nearby drainage quantities.
Hardcore Calculator
Estimate hardcore volume, tonnes, and bulk-bag buying quantities for driveways, patio bases, shed bases, and general fill work.
MOT Type 1 Calculator
Estimate MOT Type 1 volume, tonnage, bulk-bag buying quantities, and rough delivery needs for driveways, paths, and compacted sub-base layers.
Geotextile Membrane Calculator
Estimate geotextile membrane rolls, overlaps, and covered area for driveways, french drains, trenches, and separating aggregate layers.
Pipe Bedding Calculator
Estimate pipe bedding volume, tonnes, and bulk-bag buying quantities for drainage trenches before you order sand or gravel.
Quick answers
These answers are designed to resolve the last practical buying questions people usually have after running the calculator.
How do I use the Sub-Base Calculator?
Enter the footprint, compacted sub-base depth, and a realistic waste allowance, then compare the result as cubic metres, tonnes, and buying units before you order.
What changes the Sub-Base Calculator estimate most?
The biggest drivers are compacted depth, density, weak spots or level corrections in the formation, and whether the supplier is pricing by bulk bag or loose tonne.
Should I round the result up?
Usually yes. Small level corrections, compaction, and merchant minimums often justify a modest overage rather than landing exactly on the paper total.
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 Aggregate and Base Estimating project hub if the quote depends on more than one material.