Bitumen Paint Coverage Calculator | Litres & Tins
Coverage rate calculator
Bituminous paint and waterproofing coatings are sold by the litre but specified by rate — usually somewhere between 0.3 and 0.5 litres per square metre, per coat. Below is the area, the surface, and the number of coats. Above is the total volume, the coat-by-coat breakdown, and the tins to order.
Coverage calculator
Reading the numbers above
Per coat is the application rate multiplied by the area — what one pass actually uses. Before waste multiplies that by the number of coats. Total to buy adds the waste allowance, which is the figure to hand to whoever is placing the order.
The tin count is rounded up. Buying the exact litreage and running out two-thirds through the second coat costs more in a wasted trip and a visible join than the extra part-tin ever would.
Why a rate, not a depth
Paving contractors think in millimetres of thickness because asphalt is measured, laid and rolled to a depth. A brushed or sprayed bituminous coating doesn’t work that way — there’s no meaningful thickness to put a ruler on, only a rate: the volume a manufacturer states will cover one square metre in one coat, based on their own testing.
That’s why this page asks for a rate rather than a film thickness. It’s the same method used for tack coats, primers and spray seals, and it’s the number that’s actually printed on the tin or the data sheet.
What the rate looks like in practice
| Rate per coat | Per coat (12 m²) | Two coats | With 10% waste |
|---|---|---|---|
| 0.30 L/m² | 3.6 L | 7.2 L | 7.9 L |
| 0.35 L/m² | 4.2 L | 8.4 L | 9.2 L |
| 0.40 L/m² | 4.8 L | 9.6 L | 10.6 L |
| 0.50 L/m² | 6.0 L | 12.0 L | 13.2 L |
These are planning figures, not a substitute for the calculator above once you’ve entered your own area — they’re here so you can sanity-check a supplier’s quote against a rate you already recognise.
The substrate changes the first coat
A bituminous coating has to wet the surface and key into its texture before it can build a film. How much material that takes depends entirely on what’s underneath.
Smooth and sealed surfaces
New concrete, steel, GRP and previously coated surfaces are tight, with little to absorb into. These sit toward the lower end of a manufacturer’s stated range, and the first and second coats use roughly the same amount.
Standard masonry and cured concrete
Rendered block, brick and concrete that’s fully cured behave close to the rate printed on the tin — this is what most published coverage figures assume by default.
Porous and weathered surfaces
Open blockwork, aged or carbonated concrete, and anything visibly rough or chalky will draw the first coat in faster than the second. Estimate the first coat toward the top of the range; the second, once the surface is partly sealed, behaves closer to standard.
Why one coat isn’t the finished job
A single pass of a brushable bituminous coating will have thin spots — over an aggregate high point, along an arris, wherever the brush skipped. Pinholes and thin film are exactly where a waterproofing membrane fails first, and they’re invisible until the water finds them.
Two coats, applied at right angles to each other where the geometry allows it, close those gaps. It’s also why manufacturers overwhelmingly publish their coverage rate assuming two coats rather than one — treat a single-coat quote as the exception that needs explaining, not the default.
Turning litres into an order
Retail bituminous paint is sold cold, in tins and pails labelled by nominal volume, and — unlike a bulk 200-litre drum of hot-filled road bitumen — that nominal figure is what’s actually inside. There’s no equivalent of the hot-fill shrinkage that makes a bulk drum run light; a 20-litre pail of coating holds 20 litres.
What still needs rounding is the tin count itself. Ordering the exact calculated litreage from a supplier who only sells in 5, 20 and 200-litre units means picking the next size up, which is what the container field above does automatically.
Worked example
A 6 m × 4.5 m flat concrete roof, cured and in reasonable condition — standard substrate, rate 0.40 L/m² — two coats, 10% waste, priced at $6.50/L.
- Area: 6 × 4.5 = 27 m²
- Per coat: 27 × 0.40 = 10.8 L
- Two coats: 10.8 × 2 = 21.6 L
- With 10% waste: 21.6 × 1.10 = 23.76 L → round up for ordering: 24 L
- Containers: two 20 L pails cover it with roughly 16 L held in reserve for touch-ups and the next job
- Cost at $6.50/L on the 23.76 L actually needed: 23.76 × 6.50 ≈ $154
Where an estimate like this can drift
Brush application typically uses more material than spray, because a brush leaves a thicker, less even film — if you’re spraying, take the lower end of the rate range as a starting point. Ambient temperature matters too: bituminous coatings thin and spread more easily in warm weather and go on heavier when it’s cold, which shows up as a higher effective rate on a chilly site.
None of this replaces the coverage figure on the product you’re actually using. This page gets you a defensible number before that data sheet is in hand, and a way to check the order once it is.
Related to this calculator
Common questions on bitumen paint coverage
How many litres of bitumen paint do I need per square metre?
Most bituminous waterproofing coatings sit between 0.3 and 0.5 litres per square metre, per coat, depending on the product and the substrate. At two coats, budget for roughly double that per square metre before waste.
How many coats of bitumen paint does a surface need?
Two, as a working minimum for anything expected to hold water out. A single coat is thin enough in places to leave pinholes, which is where a waterproofing job tends to fail first.
Does a porous surface use more bitumen paint?
Yes. Blockwork and aged, weathered concrete draw the first coat in faster than a sealed or metal surface, so it’s worth pricing the first coat at the upper end of the rate range rather than averaging it with the second.
Is a bitumen paint tin filled to its stated volume?
Yes — retail tins and pails are filled cold and labelled by nominal volume, so a 20-litre pail holds 20 litres. That’s different from bulk 200-litre drums of hot-filled road bitumen, which run light once they cool.
Can I use this on a roof as well as a wall or foundation?
Yes, provided the coating is a brushable or sprayable bituminous product rather than a torch-on or self-adhesive membrane. Flat and low-slope roofs, foundations, retaining walls and water tanks are all coated by the same rate-and-coats method — if you’re specifying a sheet membrane instead, the roof sheet calculator linked above is the right tool.
© 2026 bitumencalculator.org. Coverage rates reflect the range typically published on manufacturer data sheets; the figure on your product’s own data sheet always takes priority over the defaults here.