Area (if the surface area is known, use it for length and make width 1)
Depth (total thickness laid, all courses combined)
| Volume | Amount |
|---|
Compacted density (typical figure - edit if your supplier quotes different)
How this calculator works
Tarmac is ordered by the tonne, so this calculator first finds the laid volume and then applies the compacted density. It multiplies length by width by depth, converting the depth from millimetres to metres; if the area is already known, enter that figure as length and use 1 for width. The default density is around 2.4 tonnes per cubic metre, the middle of the 2.3 to 2.5 t/m3 range typically quoted for rolled hot-lay tarmac; use your supplier's own figure if they state one. A waste allowance on top covers compaction, spillage and an uneven sub-base, and 5 to 10% is typical for most driveway and footpath jobs.
How thick should a tarmac driveway be?
The right depth depends on what's underneath and how the job is built up. A full driveway build-up over a prepared sub-base typically runs to around 100mm of tarmac in total: a 50-60mm binder (base) course that does the structural work, topped with a 25-40mm surface (wearing) course that gives the finish. If you're only resurfacing an existing, sound driveway and laying surface course alone over what's already there, 25-30mm is the usual figure. Footpaths carry far less load and are usually laid at 20-25mm, while car parks that see heavier or more frequent vehicles are typically built up to 100-150mm. These are typical figures, not a specification - ground conditions, drainage and the sub-base underneath all affect what a particular job actually needs.
Tarmac vs asphalt: is it the same thing?
In everyday UK usage, yes - "tarmac" and "asphalt" are used interchangeably for the black, bound stone surfacing laid on driveways, footpaths and roads, and this calculator treats them as the same material. Technically the terms have slightly different origins (tarmac originally referred to tar-bound macadam, while modern surfacing is a bitumen-bound asphalt), but no UK driveway supplier or contractor distinguishes between them in practice, so use whichever term you like.
Hot lay vs cold lay
Hot-lay tarmac is delivered and laid while still hot, then rolled and compacted before it cools - this is what a full driveway, footpath or car park uses, and it's what this calculator's density figure assumes. Cold-lay tarmac (sold in tubs or bags) is a pre-mixed product for small patch repairs - potholes, cracked edges, small areas of a few square metres - where bringing in a hot-lay crew isn't practical. It's not intended for laying a new surface from scratch and isn't what this calculator is for.
What affects the cost of a tarmac driveway
This calculator deliberately doesn't estimate cost, because tarmac pricing varies too widely by region, contractor and job specifics to give an honest figure. What it does give you is the volume and tonnage that feed into any quote, so you can sense-check what you're being quoted against. The main factors that drive cost are:
- Total area - the biggest single factor, since tarmac is priced and bought by the tonne
- Depth and build-up - a full binder-plus-surface job uses roughly double the material of a surface-only resurface
- Excavation - digging out an existing driveway or turf before laying a new sub-base adds labour and waste removal
- Edging - kerbs, block paving borders or timber edging to contain the tarmac and give it a finished edge
- Drainage - falls, channels or soakaways needed to keep surface water off the tarmac and away from buildings
- Access - how easily a tipper lorry and roller can reach the site affects labour time
Related tools
Building up a new sub-base before the tarmac goes down? Most driveways need a layer of compacted stone, commonly MOT Type 1, underneath the bound courses - the aggregate calculator works out the hardcore needed for that using the same area-and-depth approach as this page.
FAQ: worked example
How much tarmac do I need for a 5m × 6m driveway? At the full build-up preset of 100mm, the raw volume is 30 × 0.1 = 3 m3 (area 5 × 6 = 30 m2). At the default 2.4 t/m3 density that's 3 × 2.4 = 7.2 tonnes before waste. Adding the default 10% waste allowance takes the volume to 3 × 1.1 = 3.3 m3, which is 3.3 × 2.4 = 7.92 tonnes, shown rounded as 7.92 t.
How much tarmac do I need per square metre? At 100mm depth, each square metre needs 0.1 m3 before waste allowance, which is 0.24 tonnes at the default density. Multiply by your area and add your waste allowance, or just enter your dimensions above.
Does this include the sub-base? No - this calculator covers the tarmac courses only. The compacted stone sub-base underneath is a separate material and quantity; use the aggregate calculator for that.