Hypothetical: cat breaking lid, Glass in fish tank


So, I've been trying to train my cat to never set foot on the top of my fish tank, and so far so good, but now there's a bookshelf beside my tank.

Let's say theoretically, she jumps down onto my glass tank top from up there. How likely is it that she could break the lid of my tank, and would it shatter or just break? Barring the obvious wellbeing of my cat, would there be any huge worries? And how would I deal with shattered glass in my tank?

Of course, this hasn't happened and is hypothetical, but I like to be armed with knowledge. Maybe I'd like to hear how likely it is that the weight of a cat can break the glass untrimmed top of a fish tank, too.
  • Moderator


Are we talking about Garfield or a normal sized cat. Also can it knock the glass in the tank or on the floor.


I worked with glass before I retired.

Almost all cheap tanks are “float”glass . It breaks into big chunks like a Coke bottle or cracks in two.

Very few glass aquariums are “ toughened”glass that breaks like an old fashioned car windscreen.

Even float glass is very difficult to break from a side impact. It is however very easy to break from an edge impact.

In my opinion a very large dog could not break a glass lid by jumping on it.
You can however break glass easily by sliding a lid as you close it and tap an edge.

Having had the opportunity to break tons of glass, literally tons at a time from multiple truck loads taken to the rubbish dump I speak with experience .

Let me put it this way . It would be impossible to break a glass lid with a dead cat. You could throw it as hard as humanly possible. You could shoot it out of a canon .
You can however break glass very easily on an edge. Not with a dead cat but with a soft tap from a hammer ON THE EDGE.

You can relax a cat can’t break a lid by jumping on it. Even a very big cat. Even a cat with boots on.


With a thick enough piece of glass it is nearly impossible, but I've had a cat that broke a piece of 1/8 inch glass I was using as a lid. She had been walking around the fishroom on the tops of the tanks, as I keep all my tanks covered. Lids were custom fit because I cut them myself, from a supply of 1/8 inch panes I had picked up in an auction. This particular piece had developed a stress crack, and on this particular day she stepped right in the middle of it. It was a long 20 gallon tank, the glass broke into a few large pieces, easily removed. The cat took a bath, and wouldn't even go near the fish room again after that.


If you are worried about it, you could replace the glass lid with egg crate plastic - especially if there’s enough splashing from the filter to put the cat off the idea of jumping on there. For some reason, my cats, who are all about jumping onto high places, have never tried to get on the tanks.
  • Thread Starter


Thank you so much! I will rest easy knowing my ten pound cat can't break the glass on my tank. I'm really happy to know that even if it broke it wouldn't probably cause harm to my fish.
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