# How much windscreen adhesive a car actually takes

> Bead cross-section, cartridge maths and why an 8×10 mm triangle is 40 mm² — the calculation that turns 'one cartridge per car' into a number.

Updated: 2026-11-10 · Source: https://karmindadhesive.com/resources/windscreen-adhesive-bead-geometry/

A typical passenger-car windscreen takes 300–450 ml of adhesive. That is roughly one 310 ml cartridge plus a little, or one 400 ml sausage — and it follows from geometry, not from a rule of thumb.

## The bead is a triangle in cross-section

Most bonded glazing uses a triangular or trapezoidal bead, roughly 8–10 mm wide at the base and 10–12 mm high. Take 8 mm × 10 mm as a working example:

```
area = (base × height) / 2 = (8 × 10) / 2 = 40 mm²
volume per metre = 40 mm² × 1000 mm = 40,000 mm³ = 40 ml/m
```

A 4.5 m perimeter windscreen (a mid-size car) therefore needs about **180 ml** at that section. A large SUV at 5.5 m needs 220 ml. A bus windscreen at 8 m with a 10 × 12 mm bead needs:

```
area = 60 mm² → 60 ml/m → 480 ml
```

## Why the real figure is higher

Three losses sit on top of the geometry:

- **Nozzle priming and purging** — 10–20 ml per cartridge.
- **Bead variation** — a hand-held gun varies section by 10–20% along a run.
- **Cut-off waste** — the last 5–8% of a cartridge is hard to extrude.

Add 15–25% and a mid-size car lands at 210–230 ml, which is why one 310 ml cartridge covers a car with margin and a 400 ml sausage covers a large SUV.

## What this means for ordering

| Vehicle | Perimeter | Bead | Calculated | Order allowance |
|---|---|---|---|---|
| Compact car | 4.0 m | 8 × 10 mm | 160 ml | 1 × 310 ml |
| Mid-size car | 4.5 m | 8 × 10 mm | 180 ml | 1 × 310 ml |
| SUV / van | 5.5 m | 8 × 10 mm | 220 ml | 1 × 310 ml |
| Bus / coach | 8.0 m | 10 × 12 mm | 480 ml | 2 × 310 ml or 1 × 600 ml |

The numbers are arithmetic from the bead section, not a manufacturer's consumption claim. Your vehicle maker's bead profile overrides them.

## The mistake this calculation prevents

Bays often buy cartridges by "one per car" and then run short on vans and buses, or over-order for compact cars. The other failure is starting a bead and stopping: a discontinuous bead at a corner is the most common leak path, and it happens when the gun runs dry mid-perimeter.

## Triangular, trapezoidal or rectangular

The triangle is an approximation of what a gun actually lays down. Real beads are closer to a trapezoid, and the difference changes the volume by 10–20%.

| Profile | Section at 8 mm base, 10 mm height | Volume per metre |
|---|---|---|
| Triangle (base × height ÷ 2) | 40 mm² | 40 ml |
| Trapezoid (top 4 mm, base 8 mm) | 60 mm² | 60 ml |
| Rectangular (8 × 10) | 80 mm² | 80 ml |

A gun with a triangular nozzle and a steady hand produces something between the first two rows. That is why the calculation should be treated as a floor, and the 20% allowance is not padding — it is the difference between the drawing and the bead.

## Cost per car, not per cartridge

Once the volume is known, the adhesive cost per vehicle follows directly.

```
mid-size car, 180 ml calculated, 20% allowance → 216 ml
at USD 6.00 per 310 ml cartridge → USD 4.18 per vehicle
at USD 9.00 per 400 ml sausage  → USD 4.86 per vehicle
```

The cartridge is cheaper per vehicle, and the sausage is faster per vehicle. For a bay doing eight cars a day, the sausage's higher unit price buys fewer gun changes — which is a labour saving, not a material cost. The comparison that matters is cost per finished vehicle including the interruption, not price per millilitre.

For a bus at 480 ml, the arithmetic flips: two cartridges mean two chances of an interruption at a corner, and a 600 ml sausage covers the perimeter in one pass.

## What this means for buyers

1. Calculate at your actual bead section, not at a supplier's average.
2. Add 20% for purge and variation; running out mid-bead is worse than a spare cartridge.
3. For buses, buy 600 ml sausages and a sausage gun; two cartridges per vehicle doubles the interruption risk.
4. Ask the vehicle maker for the bead profile before optimising cost per car.