How big can windshield damage be and still be repairable?

Generally windshield glass damage can be repaired as long as it is less than 1.5 inches in diameter. Cracks less than 20 inches long can also usually be repaired.

It is important to remember, however, that windshield glass shouldn't always be repaired. Sometimes it needs to be replaced. If the damage is in the driver's acute line of sight, if the damage spreads to the inner layer of class, if the cracks extend all the way to the edges of the windshield in various directions, if the damage is more than one year old - all of these are conditions in which it may be a better idea to simply replace the windshield. Especially in those cases where driving with the existing damage would be illegal - these laws are there primarily for your safety and the safety of other drivers and ought not be ignored.

However, in those cases where the damage is not in the driver's line of site and within the size limits repairing windshield glass is almost always a better choice than replacing it. It is difficult if not impossible to avoid occasional rock impacts with your windshield. You can't see them coming, and often they fall off of construction vehicles whose drivers haven't properly swept their vehicles before getting on the road. Driver's who opt to replace their windshields when they might not have to often suffer the same fate once again.

Windshield repair can also be a lot more convenient than windshield replacement. Most damage can be repaired within 30 minutes. Replacing a windshield means a specialized technician has to remove the windshield, remove all adhesive from the frame, replace the adhesive and very carefully set the windshield. On top of that the car will not be driveable for several hours.