A:Answer It depends on which lens you have.
Look on the end of the lens. There should be a description of the lens, such as EF 75-300 1:4.0-5.6 IS. That is the size of type / size of your lens.
There will be another number, usually opposite the lens description. It will be something like 58, 63, or other number. That is the diameter of the lens. THAT is the number you need if you buy an accessory for the lens; such as lens cap, filters, or a hood. This specific lens hood is for a 58 mm diameter lens.
Most kit lenses (lenses that come with the lower end cameras) are 58 mm. Usually, the better the lens, the larger the diameter.
