Measures 15 X 20 inches (38 X 51cm), perforated down the middle so that you can tear it in half if it's too big (= two pieces of 15 X 10 inches each). You can also cut it with scissors to make dozens of smaller pieces.
Unless you have a major spill (an entire bottle of acid) each sheet will last many months.
When it comes to protecting yourself (and your furniture!) from spilling drops of acid, there are a few ways of working safely.
In many shops, they place some tissue or kitchen towel on the table, to work over, to catch any drips.
Personally, I prefer to hold a tissue in my hand as I work (see the videos).
The best method is to work over this anti-acid mat, it's made of a special acid-neutralising material. It not only makes any acid spills harmless, but even stops the fumes.
Comment about the picture: for the sake of the photo we used a dummy bottle (no acid), in real life I hope the user would be wearing protective gloves!
We tested this by filling a standard acid refill bottle with an extra-strong solution of acid, and carefully 'fixing' the bottle so that we knew it would leak.
We put the bottle in one of our leak-proof containers along with two circles of hazmat. We then left it in a car so that it bumped about until all the acid leaked out. When we opened the container, the bottle was empty, the fabric was slightly damp, there was a slight smell of acid - but no signs of actual wet acid.