How Much Tarmac Do I Need? A UK Guide

Before the numbers, a quick untangling of names, because the merchant and the search box don't always agree. "Tarmac" is technically a brand name that's become the everyday word for bituminous surfacing. What you're actually buying is asphalt — aggregate bound with bitumen — and you'll see it sold as "asphalt", "bitmac", "macadam" or "hot-rolled asphalt" depending on the supplier. For a domestic driveway the mix you want is usually a 6 mm or 10 mm surface course over a coarser binder course. The calculator doesn't care what it's called; the density is close enough across these mixes to use one figure.

Takeaway: if you ask for "tarmac" and the plant talks about "asphalt" or "AC 10 surf", you're both talking about the same driveway.

Area is the easy part — length times width. Depth is where the tonnage is really decided, and it's the number people leave out when they ask "how much tarmac for a 40 square metre drive?". For UK domestic work the usual build-ups are: footpaths and light patios at around 40 mm of compacted surfacing; domestic driveways at 50 to 70 mm total, most often a 40 to 50 mm binder course with a 20 to 25 mm surface course on top; regular vehicle or heavier use at 70 mm or more; and commercial or occasional HGV use at 100 mm or more, usually in two or three layers.

Those depths are the compacted thickness — the finished layer after rolling — which is exactly what a tonnage calculation should be based on.

Takeaway: for a normal car driveway, work to 50 to 60 mm of tarmac; anything thinner is a patio spec, not a drive.

Here's the full chain from tape measure to order. Area in m² is length times width. Volume in m³ is area times (depth in mm divided by 1000). Tonnes is volume times 2.36, which is the compacted density of asphalt in tonnes per cubic metre — most UK mixes sit between 2.3 and 2.4 t/m³. Then add wastage: 5% for a clean rectangle, 10% as a sensible default, up to 15% for lots of edges and cutting-in.

That density figure is the quiet workhorse. At 2.36 t/m³, a square metre laid 50 mm deep weighs about 0.118 tonnes — so a tonne covers roughly 8.5 m² at that depth. The coverage by depth: at 40 mm, 0.094 tonnes per m² and about 10.6 m² per tonne; at 50 mm, 0.118 tonnes per m² and about 8.5 m² per tonne; at 60 mm, 0.142 tonnes per m² and about 7.1 m² per tonne; at 70 mm, 0.165 tonnes per m² and about 6.1 m² per tonne.

Takeaway: multiply area by the tonnes-per-m² for your depth, add 10%, and you've got your order — no guesswork.

Take a driveway in a Wakefield semi measuring 10 m long by 4 m wide — 40 m² — laid as a 60 mm build-up: a 40 mm binder course and a 20 mm surface course, over a compacted Type 1 sub-base.

Volume = 40 x 0.06 = 2.40 m³. Tonnes = 2.40 x 2.36 = 5.66 tonnes. Add 10% wastage: 5.66 x 1.10 = 6.23 tonnes.

So you'd order around 6.5 tonnes — plants and grab-lorries typically deliver in round or half-tonne increments, and you round up, never down, because the last stretch of an under-ordered drive is the one that goes cold before more arrives. A typical 2026 material price from a regional asphalt plant might put that in the region of £300 to £500 for the tarmac alone, before delivery and before a penny of labour. For the full installed figure — which is a very different and much larger number — use the Driveway Cost Calculator UK.

Takeaway: a standard two-car drive at 60 mm is about six tonnes plus waste — call it six and a half to order.

If you're patching a pothole or topping a short path, ordering hot tarmac by the tonne makes no sense — you can't lay it fast enough before it cools. This is what cold-lay (or "instant repair") tarmac is for: 25 kg bags you tip, rake and tamp by hand, sold by Wickes, B&Q, Travis Perkins and most builders' merchants.

The maths is the same, just expressed in bags. A 3 m by 1 m path repair at 25 mm works out to 0.075 m³, which is 0.177 tonnes, which is about 8 x 25 kg bags with a bit of waste. As a rule of thumb, a 25 kg bag covers roughly 0.4 m² at 25 mm.

Takeaway: under a tonne or so, buy cold-lay bags; over a tonne, get a plant to deliver hot.

Most "how much tarmac" pages stop at the tonnage and send you off to order. Here's the part that actually decides whether the drive lasts: the tarmac is the thin skin on top of the job, and almost every failed domestic driveway fails because of what's underneath it, not the tarmac itself.

A driveway needs a properly compacted Type 1 (MOT) sub-base, usually 100 to 150 mm of it, whacked down in layers, plus solid edge restraints so the tarmac can't creep sideways. Skip the compaction or lay tarmac straight onto soft ground and it'll rut, crack and shove within a couple of winters no matter how good the surfacing mix was. The sub-base isn't in your tarmac tonnage — size it separately with the Gravel & Sub-Base Calculator.

A groundworker put it bluntly: he said he's never once been called back for a drive that failed because the tarmac was too thin — it's always the base that wasn't compacted properly, or edges that were never restrained. The tarmac gets the blame because it's the bit you can see cracking.

Takeaway: spend the effort on the sub-base and edges; the tarmac is the easy 20% of the job that gets 80% of the attention.

Asphalt surfacing in the UK is specified under BS 594987 (transport, laying and compaction) and the Specification for Highway Works Series 900; the sub-base follows SHW Clause 803 for Type 1. On the planning side, since the 2008 permitted-development changes a new or replacement front driveway over 5 m² in an impermeable surface like tarmac needs planning permission unless the surface water drains to a permeable area within your boundary rather than out to the public highway. Routing runoff to a border or soakaway normally keeps you inside permitted development.

Takeaway: on a front drive, plan where the water goes before you order the tarmac — it's a permitted-development condition, not an afterthought.

Enter your area and depth into the Tarmac Calculator UK and it returns the tonnes — or bags for a small repair — with wastage already built in.

Disclaimer: This guide is for planning. Actual tonnage varies with mix type, compaction, laying depth, sub-base and site conditions. Compacted asphalt density is taken as 2.36 t/m³; your supplier's mix may differ.