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Windscreen Chips and Cracks: Repair or Replace? The Full Guide
Should you repair or replace a cracked windscreen? The £2-coin rule, line-of-sight zones, crack length and edge damage explained — plus what insurance covers and when to act fast.
Written by the MyCarGlass team. Reviewed by Manish Patel, founder, and Robert Webster, windscreen expert — fitting glass since 1995. Last updated 20 June 2026.
A stone flicks up, there’s a sharp crack, and now there’s a star in your glass. The question every driver asks next is the right one: can this be repaired, or does the whole windscreen need replacing? This guide gives you a clear, honest decision framework — the size rules, the line-of-sight test, where the damage sits, and how quickly you need to act — so you know what to expect before anyone quotes you.
For the work itself, see windscreen repair and chip repair; for a full new screen, windscreen replacement.
Repair or replace — what’s the quick answer?
As a general rule, small chips and short cracks away from the driver’s line of sight and away from the glass edge can be repaired, while large, long, deep, edge-reaching or line-of-sight damage needs replacement. Repair is faster, cheaper, keeps your original factory glass, and is often free under insurance — so it’s the preferred option whenever it’s safe and effective. Replacement is the right call when a repair couldn’t restore strength or clarity well enough to be trusted.
The four things that decide it are size, location, depth and timing. Let’s take each.
The size test: the £2-coin and bank-card rules
A widely used rule of thumb across the trade:
- A chip is generally repairable if it’s roughly smaller than a £2 coin (about 26 mm).
- A crack is generally repairable if it’s shorter than around 15 cm — roughly the long edge of a bank card plus a little more — though many repairers set their practical limit shorter than this.
- Multiple chips can sometimes be repaired in one visit, depending on how many and where they are.
These are guides, not guarantees: a chip slightly under the coin size but very deep, or sitting badly, may still need replacement, while a clean chip is an easy repair. The honest assessment happens when a technician sees the damage.
The line-of-sight test: where is the damage?
Location matters as much as size — and this is where the law comes in. The MOT and roadworthiness rules divide the windscreen into zones based on the driver’s view:
Zone A is a band 290 mm wide, centred on the steering wheel, within the area swept by the wipers. This is the driver’s critical forward view. Damage here is held to a much stricter standard: in Zone A a single damaged area must sit within a 10 mm circle to be acceptable. So even a small chip directly in front of the driver can mean the screen needs replacing, because a repair may leave slight optical distortion right where you’re looking.
Zone B is the rest of the swept area. Here a single damaged area must sit within a 40 mm circle. There’s more tolerance for repair away from the driver’s eyeline.
The practical upshot: a chip the size you’d happily repair in the passenger-side corner might require a full replacement if it’s directly in your line of sight. We explain the legal and MOT side fully in Is driving with a cracked windscreen legal?
The edge rule: damage near the perimeter
Damage within about 5 cm of the edge of the glass is usually a replace, not a repair. The edge is where the windscreen carries the most structural stress and where it bonds to the body, so cracks there spread quickly and a repair is far less reliable. A crack that reaches two points at the edge of the swept area is treated as rendering the windscreen insecure — that’s a replacement.
Does the type of damage matter?
Yes. Technicians describe damage by pattern — a bullseye (a neat circular cone), a star break (legs radiating out), a combination break, a half-moon, and a long crack line. Clean bullseyes and small stars repair well. Long single cracks, complex combination breaks, anything contaminated with dirt or water, and damage that has already started “legging out” are more likely to need replacement. Depth counts too: damage through only the outer glass layer repairs well; damage that has penetrated deep or reached the inner layer generally can’t be repaired safely.
“The honest answer is that timing decides more cases than size. A small star break we could repair on Monday becomes a foot-long crack by Friday because the owner kept driving, kept blasting the heater, hit a few cold nights. Call the day it happens and you give yourself the cheap, quick option.” — Manish Patel, founder, MyCarGlass
How fast do I need to act?
Quickly — this is the factor drivers most underestimate. A stable chip can run into a crack with very little provocation: a temperature swing (cold night, hot demister), a speed bump, a pothole, or a slammed door can be enough. Dirt and water working into the chip also make a later repair less effective and less invisible. The sooner damage is seen, the more likely it can be repaired rather than replaced. In the meantime, avoid extreme temperature changes, don’t blast hot air straight at a cold chip, and a piece of clear tape over the chip keeps dirt and moisture out until your appointment.
“If you can’t get it looked at straight away, put a small piece of clear sticky tape over the chip — not over your line of sight — just to keep the rain and grit out. It genuinely improves the odds of an invisible repair when you do get to us.” — Robert Webster, windscreen expert, MyCarGlass
What does a repair actually involve?
A chip repair takes around 20–30 minutes. The technician cleans and dries the damage, injects a clear resin under vacuum and pressure to fill the break and bond the layers, then cures it hard with UV light and polishes it flush. Done early, the repair is structurally sound and visually close to invisible. Best of all, it preserves the original factory-bonded glass and seal — no disturbance to trim, sensors or the windscreen’s structural role.
What does replacement involve — and what’s different on modern cars?
Replacement means removing the old screen, preparing the aperture, and bonding in correct-specification glass with the right adhesive and a proper safe drive-away time. On modern cars there’s a crucial extra step: if your car has a forward-facing camera for lane-keep assist, automatic emergency braking or adaptive cruise control, the camera must be recalibrated to manufacturer specification after the new glass goes in. Skipping that leaves safety systems misaligned. See ADAS calibration for how that works, and Windscreen replacement by vehicle make for what changes brand to brand.
What does it cost — and will insurance pay?
Repair is far cheaper than replacement, and frequently free under insurance: many comprehensive policies cover glass repair with the excess waived, because a repair saves them a much larger replacement bill. Replacement is covered too but carries a glass excess (often a fixed amount set by your policy), and adds the cost of glass and calibration where needed.
As a rough guide to current cash prices: a chip repair typically runs around £40 to £120 if you pay directly (often £0 under insurance), while a standard windscreen replacement on a mainstream car generally falls in the £250 to £450 range. Premium and ADAS-equipped cars can run from around £500 to well past £1,000–£2,000 once sensors, heating, acoustic glass and calibration are involved, with ADAS camera calibration adding roughly £150 to £400 (and more on complex systems). If you claim a replacement, your glass excess is usually in the £75 to £150 region depending on your policy. Prices correct as of June 2026 and shown as general market ranges — your exact price depends on your vehicle and glass specification.
We’re approved by major insurers — Aviva, Allianz, LV=, AXA, NFU and the AA — and can handle the claim for you. The full breakdown of glass excess and no-claims is in Does windscreen replacement count as a claim?; for cash prices see our prices and the replacement cost guide.
Do shop-bought DIY repair kits work?
Sometimes — but with real caveats, and we’d rather be straight with you than sell you a job. A cheap kit can stabilise a small, fresh, simple chip (a clean bullseye, not in your line of sight) and stop it spreading, which is better than doing nothing if a professional repair genuinely isn’t available for a few days.
The problems are practical. DIY kits rarely pull a full vacuum, so they often trap air and leave a visible blemish rather than the near-invisible finish a professional resin-injection achieves. They struggle with star and combination breaks, and they can’t safely handle anything deep, dirty or near the edge. Most importantly, once a kit’s resin has cured in the break, a professional often can’t redo it cleanly — the DIY resin has to be drilled out, and the result is usually worse than if it had been left for us. And a kit does nothing for the decision that matters most: whether the damage is in Zone A or otherwise a replace-not-repair case.
Our honest take: if it’s in your line of sight, deep, spreading, or you want it to look right, skip the kit. A professional repair is quick, often free under insurance, and gives the strongest, clearest result — and we’ll tell you for free whether it’s repairable at all.
Repair or replace: the decision at a glance
| Factor | Lean towards repair | Lean towards replace |
|---|---|---|
| Chip size | Smaller than a £2 coin | Larger than a £2 coin |
| Crack length | Short (≈ under 15 cm) | Long |
| Location | Away from driver’s eyeline (Zone B) | In Zone A / driver’s line of sight |
| Edge | Clear of the edge | Within ~5 cm of the edge, or reaching two edge points |
| Depth | Outer layer only | Deep or through to inner layer |
| Timing | Caught early, clean and dry | Old, spread, dirty or contaminated |
Quick answers
Will a windscreen repair be visible afterwards? Done early on a clean chip, a professional repair is usually close to invisible — you may see a faint mark up close. The longer dirt and moisture sit in the break, the more visible the final result, which is why acting fast matters.
Does a windscreen repair last — and does it weaken the glass? A proper resin repair is permanent and restores strength to the damaged area; it doesn’t weaken the glass. It bonds the layers and stops the chip spreading, and it won’t “pop back out” later.
Will my car still pass its MOT after a repair? Yes, provided the repaired area meets the MOT limits for its zone (within 10 mm in Zone A, 40 mm in Zone B) and doesn’t significantly affect the driver’s view. A good repair brings borderline damage back within spec; a poor patch in your eyeline may not.
Can a long crack be repaired? Usually not. Beyond roughly 15 cm, reaching the edge, or in your line of sight, a crack typically needs replacement rather than repair — both for strength and for clarity.
Can the same chip be repaired more than once? No — a break is repaired once. If a DIY kit or a poor earlier attempt has already filled it, the glass usually has to be replaced rather than re-repaired.
The bottom line
If it’s small, shallow, clean, away from your eyeline and away from the edge — repair it, fast, and you’ll likely keep your glass and pay little or nothing. If it’s large, long, deep, in your line of sight or at the edge, replacement is the safe and legal answer. When in doubt, get it assessed early: the longer you wait, the more the decision gets made for you.
We’re family-run, fitting glass since 1995 — over 30 years — with in-house fitters, a 7-year guarantee, and a 5.0 rating on the road to 1,000+ 5-star reviews. Phones are manned until 7pm with an AI assistant after hours. Get it assessed or book a repair, or call 020 8909 2300.
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