Another good method is to separate the quantity you purchased into properly measured smaller containers say half for each halves for each half of the garage. That way you will know how much to use for tht area. This method works well with flecks too so you don't run out.
Be careful though if using a 2 part epoxy to not mix until you need to as they have listed working times, especially a 100% solids type epoxy. Keep a moisture cured product sealed until use.