Quick answer
Window screen mesh is the woven netting in a window or door screen, rated by its mesh count, the number of openings per inch in each direction, which sets how small an insect it can keep out.
A higher count means smaller holes, and CDC advises screens on windows and doors, with holes repaired, to keep mosquitoes outdoors. Biting midges, or no-see-ums, are small enough to pass through regular window screen.
Quick facts
The key facts about Window Screen Mesh, with sources:
- Common spec
- 18x16 mesh with 0.011-inch wire (manufacturer data) 6
- Opening size of that spec
- About 0.045 by 0.052 inches; 66.1% open area 6
- Tiny biting midges
- Adults 0.04–0.08 inch long; regular window screen does not keep them out 5
- Rodent-proof window screen
- 19-gauge, 1/2-inch mesh wire cloth on windows that open near the ground 4
Key takeaways
- Mesh count is the number of openings per inch; higher numbers mean smaller holes.
- Standard insect screen, often sold as 18x16, is the common spec for flies and mosquitoes.
- Tiny biting midges, or no-see-ums, pass through regular window screen and need special no-see-um screen.
- A torn or loose screen fails no matter what the mesh count is.
- Insect screen does not stop rodents; low windows need metal wire cloth.
Screen mesh, explained
A window screen is a frame holding a woven net, the mesh, whose job is to let a breeze in while keeping insects out.
Mesh is described by its mesh count, two numbers such as 18x16 that tell you how many openings fit in one inch in each direction.
The thickness of the wire matters too, because thicker wire leaves less room for the holes.
A manufacturer data sheet for 18x16 aluminum screen with 0.011-inch wire lists openings of about 0.045 by 0.052 inches and 66.1% open area 6.
CDC’s mosquito advice is simple: use screens on windows and doors, and repair holes in them to keep mosquitoes outdoors 1. UC IPM recommends fine mesh screens in good repair for mosquitoes, and well-fitted screens to limit house flies 2 3.
Insect screen vs. exclusion mesh
Insect screen is thin and made for flying bugs. Exclusion mesh for rodents and wildlife is heavier metal wire cloth. UC IPM specifies 19-gauge, 1/2-inch wire cloth for low windows against rats 4.
How mesh keeps insects out
- The weave sets the hole size. Openings per inch and wire thickness together decide how big each hole in the weave is 6.
- Insects bigger than the hole are blocked. Flies and mosquitoes are stopped by intact standard screen, per UC IPM and CDC guidance 3 1.
- Smaller insects pass. UF/IFAS says regular window screens do not exclude biting midges, whose adults are only 0.04 to 0.08 inch long 5.
- The frame must seal. Gaps around the frame or tears let insects bypass the mesh entirely 2.
- Air still flows. Open area is the share of the screen that is hole, so finer mesh means less airflow through the window.
Opening ≈ (1 ÷ mesh count) − wire diameter
mesh count- openings per inch in one direction
wire diameter- thickness of the wire, in inches
For 18 per inch and 0.011-inch wire: 0.0556 − 0.011 ≈ 0.045 inch, matching the manufacturer data sheet.
Source: [6]
Types of screening
| Type | Used for | Source note |
|---|---|---|
| Standard insect screen (often 18x16) | Flies, mosquitoes, general use | Common spec on manufacturer sheets 6 |
| No-see-um screen | Tiny biting midges | Openings small enough to exclude midges; not commonly sold for windows 5 |
| Aluminum wire screen | Durable insect screen | Data sheet lists ASTM B134 alloy and ASTM E2016 weave 6 |
| Metal wire cloth, 1/2-inch mesh | Rats at windows near the ground | 19-gauge per UC IPM 4 |
| Vent screen (wire cloth) | Crawl space and foundation vents | 16-gauge 1/2-inch wire cloth or 18-gauge expanded metal 4 |
Worked example: why a higher mesh count means smaller holes
This is an example only, in which we apply the opening formula to different mesh counts at the same 0.011-inch wire. The 18-per-inch row matches the manufacturer’s published opening 6; the other rows are our arithmetic.
| Openings per inch | Spacing (1 ÷ count) | Approx. opening |
|---|---|---|
| 16 | 0.0625 in | About 0.052 in |
| 18 | 0.0556 in | About 0.045 in (data sheet: 0.04456 in) 6 |
| 20 | 0.050 in | About 0.039 in |
Going from 16 to 20 openings per inch shrinks each hole by about a quarter in this example, yet UF/IFAS says regular window screen does not stop biting midges, which average about 0.06 inch long 5. Shrinking the hole only goes so far, and the trade-off is less open area and so less breeze.
Where you will see mesh specs
On a roll of screening or a replacement screen package, look for the mesh count (such as 18x16), the material and sometimes the wire diameter, and some data sheets cite ASTM weave and alloy standards 6.
On a pest company’s inspection report, screens show up as “torn screen, kitchen window” or “missing screen, crawl space vent” under conducive conditions, and for mosquito jobs, a pro may note unscreened windows along with standing water. Our mosquito control guide explains the full service.
Benefits and trade-offs
What it does well
Where it falls short
- Finer mesh cuts airflow and makes it harder to see out of the window.
- Regular window screen does not stop no-see-ums 5.
- Insect screen tears easily and does not stop rodents that chew or push through.
- Gaps in the frame defeat any mesh, however fine the weave is.
What screens cannot do
- They do not keep out pests that come in on people, pets or packages.
- They do not stop rats; UC IPM says never use lightweight chicken wire and specifies metal wire cloth instead 4.
- They do not stop mosquitoes breeding in your yard; CDC says to empty standing water weekly 1.
- An insect-treated screen is a pesticide product; follow its label, and do not add sprays not labeled for screens.
Cost drivers and how long screens last
Screen cost depends on the material, the mesh count, the number and size of windows, and whether frames need repair, and finer mesh and metal wire cloth cost more than standard fiberglass or aluminum screen.
The sources cited give no fixed lifespan, because sun, pets and children wear screens out at different rates, so replace any that sag, tear or pull from the frame. We do not list prices; see the pest control cost guide and the mosquito cost estimator for yard treatment.
Choosing and fitting screen mesh
- Name the pest. Flies and mosquitoes need standard insect screen, while no-see-ums need purpose-made no-see-um screen 5. Rats at low windows call for 19-gauge, 1/2-inch wire cloth 4.
- Check the frame. Bent or loose frames leave gaps that insects can use, so fix or replace them.
- Patch or rescreen. Small holes can be patched, while large tears need new mesh across the whole frame.
- Pull it tight. The spline, the rubber cord pressed into the frame groove, must hold the mesh evenly with no loose corners.
- Screen the vents too. UC IPM lists vent grill specs for rodents 4.
No permit is needed for window screens, but escape windows in bedrooms must still open fully; do not fix screens in a way that blocks a required exit.
Screen maintenance
- Walk the house each spring and look for holes, sagging and gaps at the frame.
- Repair holes as soon as you find them; UC IPM’s mosquito tips say to repair any holes or openings 2.
- Clean screens regularly so you can spot small tears and damage early.
- Check crawl space and attic vent screens at the same time as the windows.
- No holes or tears
- Mesh tight in the frame
- No gap at frame edges
- Doors close fully with screens on
- Vent screens intact
Warning signs and when to call a pro
Signs that screens are failing: mosquitoes indoors at night, flies collecting at a window, or tiny biting insects indoors near the coast or water, and mosquitoes indoors with screens closed often mean a tear or gap somewhere.
Call a pro if mosquitoes stay heavy after screens and standing water are handled, or if you find rodent signs at windows or vents.
Mosquitoes can spread disease
Some mosquitoes spread viruses such as West Nile. Screens and removing standing water are CDC’s first steps 1. See a doctor for fever, headache or body aches after bites. Keep window screens secure where small children could push on them.
Standards and rules
No federal rule requires window screens on homes, although some local housing codes require screens on rental units in certain months; these vary by city and state.
Product standards exist: manufacturer data sheets cite ASTM E2016 for the woven wire and ASTM B134 for aluminum wire 6.
For crawl space vents, some state pest rules set limits; Georgia’s structural pest rules, for example, require vent coverings with a least dimension of no more than 1/4 inch 7. See licensing by state.
Window screen mesh vs related barriers
| Barrier | Stops | Does not stop |
|---|---|---|
| Standard insect screen | Flies, mosquitoes 3 1 | No-see-ums 5; rodents |
| No-see-um screen | Biting midges 5 | Rodents |
| Metal wire cloth, 1/2 inch | Rats at low windows and vents 4 | Small insects |
| Caulk | Insects at fixed cracks | Anything at an open window |
| Door sweep | Crawlers under doors | Flying insects at windows |
Myths about screens
- Myth Any screen stops every bug.
- Reality UF/IFAS says regular window screens do not keep out biting midges 5.
- Myth A small hole does not matter.
- Reality CDC says to repair holes to keep mosquitoes outdoors 1.
- Myth Chicken wire works for rats.
- Reality UC IPM says never use lightweight chicken wire 4.
- Myth Screens alone fix a mosquito problem.
- Reality CDC also says to empty standing water each week 1.
Where finer mesh earns its keep
Mesh choice is regional, and UF/IFAS Extension notes that regular window screens do not exclude biting midges, and that no-see-um screen has openings small enough to stop them 5.
Homes near coasts, marshes and other wet areas where biting midges are common get the most from finer mesh, while elsewhere standard insect screen in good repair is usually the fit. Our seasonal calendar shows when biting insects peak in your region.
When screen mesh matters to you
Screens are the first line against mosquitoes and flies for anyone who opens windows in warm months, and if you get tiny biting insects indoors with screens closed, consider finer mesh. If you have rats, screen low windows and vents with metal wire cloth.
Pair screens with removing standing water and sealing gaps, and see integrated pest management for how the pieces fit, and use the pest identifier if you are not sure what is getting in.
Questions about Window Screen Mesh
What does 18x16 mean on window screen?
It means 18 openings per inch in one direction and 16 in the other, and it is a common insect screen spec. A manufacturer data sheet for 18x16 aluminum screen with 0.011-inch wire lists openings of about 0.045 by 0.052 inches and 66.1% open area.
Can mosquitoes get through window screens?
Mosquitoes are kept out by intact, well-fitted insect screen, which is why CDC advises using screens on windows and doors and repairing holes. Most mosquitoes that get inside come through tears, gaps at the frame or open doors, which is why UC IPM recommends fine mesh screens in good repair.
What screen mesh keeps out no-see-ums?
You need special no-see-um screen, because UF/IFAS Extension says regular window screens do not exclude biting midges, which are usually 0.04 to 0.08 inch long. No-see-um screen has openings small enough to keep them out, though it is not commonly sold for windows and doors, so you may need to order it.
Does finer screen mesh reduce airflow?
Yes, because finer mesh has smaller holes, so less of the screen is open. The 18x16 data sheet lists 66.1% open area; higher counts with the same wire leave less, so pick the coarsest mesh that still stops the pests you actually have.
Will window screens keep mice and rats out?
No, insect screen is too weak, and UC IPM says windows that open near the ground need 19-gauge, 1/2-inch mesh wire cloth against rats, and never lightweight chicken wire, while vent grills need 16-gauge wire cloth or 18-gauge expanded metal.
How do I find holes in my screens?
Look at each screen against daylight, from inside, and check the corners and frame edges after you clean dusty screens. Fix holes as soon as you find them; CDC and UC IPM both say to repair screen holes to keep mosquitoes out.
Are screens enough to control mosquitoes?
Screens keep mosquitoes out of the house, but not out of the yard, so CDC also advises emptying, scrubbing, turning over or throwing out items that hold water once a week, since mosquitoes lay eggs in or near water. Heavy yard problems may need a mosquito control service.
Do screens help with house flies?
Yes, because UC IPM says house flies indoors have almost always come from outside, and well-fitted screens limit their access. It says sanitation plus screens should usually be enough to keep flies out of a home, without pesticides.
Do crawl space and attic vents need screens?
Yes, because vents are open holes that pests can use, and UC IPM gives rodent-proof specs for vent grills: 18-gauge, 1/2-inch expanded metal or 16-gauge, 1/2-inch wire cloth.
Some states also set rules for licensed pest companies, and Georgia’s structural pest fact sheet, for example, says crawl space vent openings must be covered with materials whose least dimension does not exceed 1/4 inch, using options such as hardware cloth or corrosion-resistant wire mesh.
Should I buy aluminum or fiberglass screen?
Both are sold as insect screen, and the right choice depends on wear, budget and looks rather than pest type.
What matters most for pests is the mesh count and a tight fit in the frame, and manufacturer data sheets for aluminum screen list the alloy and weave standards they meet, such as ASTM B134 and ASTM E2016.
Neither type stops rodents; use heavier metal wire cloth where rats or mice are the concern.
Sources
- U.S. CDC, Preventing Mosquito Bites, retrieved .
- UC Statewide IPM Program, Pest Notes: Mosquitoes (Publication 7451), retrieved .
- UC Statewide IPM Program, Pest Notes: House Flies (Publication 7457), retrieved .
- UC Statewide IPM Program, Pest Notes: Rats (Publication 74106), retrieved .
- UF/IFAS Extension EDIS, Biting Midges, No-See-Ums, Culicoides spp. (EENY-349/IN626), retrieved .
- Manufacturer data sheet, 18x16 mesh 0.011 in bright aluminum insect screen (ASTM B134, ASTM E2016), retrieved .
- Georgia Department of Agriculture, Structural Pest Division, Compliance Fact Sheet: Under-Floor Space Ventilation, retrieved .
Expert review
Written by the HyrePest Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Screen advice follows CDC and UC IPM Pest Notes 7451, 7457 and 74106.
Mesh dimensions are from a manufacturer data sheet, as no extension source publishes them; the other mesh-count rows are our arithmetic with the stated formula. Biting midge size and screen advice come from UF/IFAS EDIS publication IN626.
The vent rule is from the Georgia Department of Agriculture. No prices are given.
Suggest a correction. We fix errors and say what changed.