A clear reference showing what standard, fine, and ultra-fine mesh can block — and what can slip through.
All mosquito screens rely on one simple concept: the mesh opening must be smaller than the insect trying to pass through. This guide explains insect sizes in calm, practical terms so you can choose the mesh that fits your needs.
| Mesh Type | Approx. Opening Size | Typical Use |
|---|---|---|
| Standard Mesh (18×16) | ~1.1–1.4 mm | General household use |
| Fine Mesh (20×20) | ~0.9–1.0 mm | Humid climates & small insects |
| Ultra-Fine Mesh (30×20 or tighter) | ~0.7–0.8 mm | No-see-ums, midges, sandflies |
These measurements vary slightly between brands, but they provide a reliable reference point.
Approximate body widths below help determine what can pass through each mesh type.
| Insect | Approx. Body Width | Can Standard Mesh Stop It? | Notes |
|---|---|---|---|
| Mosquito | 2.5–4 mm | Yes | Standard mesh is made for them. |
| Housefly | 4–7 mm | Yes | Easily blocked. |
| Fruit fly | 1.5–3 mm | Yes | Small, but still too big to pass. |
| Midge / No-see-um | 0.6–1.0 mm | Sometimes | Requires fine or ultra-fine mesh for full blocking. |
| Sandfly | 0.8–1.2 mm | Sometimes | Fine mesh recommended in coastal regions. |
| Gnats | 1.0–1.5 mm | Mostly | Occasionally slip through worn mesh. |
| Thrips | 0.2–0.5 mm | No | Too small for residential mesh; rarely attracted indoors. |
Even with the right mesh size, tiny insects can enter under specific conditions:
These issues are more significant than the mesh size itself in most homes.
Standard mesh (18×16) is enough for typical mosquitoes and flies.
Fine mesh (20×20) reduces small-insect entry during peak humidity hours.
Ultra-fine mesh is the safest choice, especially around sleeping areas.
Check for micro-gaps, airflow drafts, and lighting that may be drawing insects toward the screens.
See: When screens aren't enough →
Choosing the right mesh is less about perfection and more about understanding the insects in your area.
For deeper guidance, you can continue with: