Paving

Sub-base calculator

Measure your area, enter the depth you are using, and work out the sub-base volume before you buy.

Start with what you can measure. For a product figure, use the label or product page. Your practical estimate appears first; the technical detail sits below it.

01Tell us what you can measure

Add your measurements, then check the steps before you buy.

Units

Step 1 · Your area

Start with a length and width you can measure. We work out the area for you. If you already know the total volume, choose the shortcut instead — it does not need an area or depth.

How would you like to start?

Area01

Area name optionalHow do you know this area?

Length mWidth m

Step 2 · Depth you're using

Use the depth already shown in your plan, product guidance or advice you've been given. Calculator.Shop does not recommend a depth.

Depth you're using Enter the value you already have.Depth unit

02Your volume estimate

Add your area and the depth you are using to see the volume.

Measure an area, enter the depth you are using, and we will work out the volume in cubic metres before any product conversion. Suppliers may sell by tonne, bag or bulk bag, so use the optional section only when you have those product details.

What this does not cover: Quantity estimate only from the area, depth and optional product values you provide. It does not choose a sub-base product or depth, or assess ground, drainage, falls, excavation, compaction, suitability, load capacity, patio or driveway design, foundations, Building Regulations or installation.

See the working

How we worked it out

Follow the short steps from your measurements to the final rounded quantity.

Add your measurements above to see how we worked it out.

Where the numbers come from

A quick guide to this estimate.

You enterMeasured areas or a reliable total volume, the depth you are already using and any allowance you choose.
You can change:The areas or volume you enter, the depth you are already using and any allowance you choose.
From the product details you enterA product-unit volume, stated product coverage, supplier density or tonnes-per-volume figure you choose to enter.
Worked out hereWe total the areas you enter, multiply them by the depth you are already using, then apply an allowance or product conversion only when you choose one.

Measuring tips

What to measure

Measure each rectangular area by length and width. Add another area only when it belongs in the same quantity calculation. Use the direct-area option when you already have a reliable area. Then enter the depth you are already using; this calculator does not choose one.

Measure the finished surface or dimensions used by this tool. Keep a note of the values you enter.

Worked example

See it in practice

A 4 m × 3 m area is 12 m². At a depth already given as 50 mm (0.05 m), 12 m² × 0.05 m = 0.60 m³. The measurements and depth are example values only, not a construction recommendation.

Keep a noteUse the actual values from your own plan, product guidance or supplier information; the figures above are only an example.

Before you buy

Three quick checks

01
Measure only the areas you intend to fill with sub-base.
02
Use the depth already shown on your plan, product guidance or advice you have been given.
03
Keep the neutral m³ result unless you have a product or supplier figure to convert it.

Quick answers

Useful to know

How much sub-base do I need?

Measure the area or enter a reliable measured area, then enter the depth you are already using. The calculator multiplies those values and gives the volume in m³ before any product conversion.

Can this tell me how many tonnes I need?

Only when you enter a tonnes-per-cubic-metre figure or supplier density for the specific product you chose. Density varies, so Calculator.Shop never assumes one.

Does this tell me which sub-base or depth to use?

No. It calculates quantity from your geometry and already decided values. Ground conditions, drainage, falls, compaction, product suitability, patio or driveway design and installation need separate project-specific checks.

Method and checks

How this estimate is put together.

Calculation checked

Last checked 20 October 2026 · review again by 20 October 2027. The method version is available in the detail below.

The calculation steps and rounding are shown and have been checked. Before buying, check the coverage, pack size or other product detail you entered.

Keep in mind: sub-base quantity estimate only; not ground, drainage, material, depth or installation design. This remains a planning estimate, not a design or approval.

Details that can vary: No universal sub-base density, tonnes conversion, allowance, product, depth or layer build-up is supplied.

Check the product details: A product-unit volume, stated product coverage, supplier density or tonnes-per-volume figure you choose to enter. Calculator.Shop does not choose or supply these figures.

See sources, values you can change and method history

Sources for this method

Calculating the area and the perimeterMathplanet / Mattecentrum · mathematical definition · Public reference, accessed 17 October 2026Supports: Rectangle area (length × width) where a Calculator.Shop tool asks for a measured section. Pack, roll or board coverage and any extra allowance are values the visitor enters.
VolumeWolfram MathWorld · mathematical definition · Public reference, accessed 17 October 2026Supports: Cuboid and cylinder volume derivations using common linear units.

Values you can change

The areas or volume you enter, the depth you are already using and any allowance you choose.

What we check

The stated calculation steps, rounding and limits of this estimate.

When we check it again

Before the area, depth, allowance or product-conversion method changes; Before a density, tonnes or product value is presented as anything other than visitor supplied; When the stated ground, drainage, depth or installation safety boundary changes.

Method history

v1.0 · 2026-10-20First Sub-base Calculator method: neutral geometry first; product conversion only from visitor or supplier values.

See how we verify calculations