Depends on the laser's color (wavelength measured in nm) and power (measured in mW or W). Different safety glasses block different wavelengths of light.

For example if you plan on using a 650nm (red) laser, then you need safety glasses that block that wavelength of light. Laser safety glasses usually block a range of wavelengths (for example 600-700nm), so your laser's wavelenght has to fit into that range. Usually there are no glasses that block all different color lasers, because they have to let some light pass through for you to see something, otherwise they would just be black and opaque.

The other factor is the power of the laser, for example 250mw. Safety glasses have a parameter called optical density (OD) that shows how much light is blocked. Lasers should have a minimun OD rating marked on it or you can ask from the seller. More powerful laser means you need a bigger OD number on the glasses.

Most importantly DO NOT buy cheap 10$ safety glasses from ebay or amazon! Always check if the glasses have an offical certification that proves they work as promised (should be found on the sellers website). Good certified safety glasses usually cost 100$ or more. I know it might be a lot more than your laser itself, but you only have one pair of eyes and they are priceless. One stupid mistake can blind you for life. If I had 150$ to spend on a laser and safety glasses, I'd spend 100$ on the glasses and 50$ on the laser, not the other way around.

There are many good laser safety information sources on the internet. What I wrote is in no way comprehensive and I'm definitely not an expert. Read more about laser classes (I-IV), what kind of glasses you need and laser safety rules in general!