If you are asking because you have a road bike, the first step is do do some measuring to find the maximum size tire that can fit in your frame (chainstays, fork). You need at least 3-4 mm clearance, according to the info I got when I put larger tires on my bike.
NB: maximum inflated tire width doesn't necessarily match the published width number... i.e. a '28 mm' tire could inflate to 30 mm or 26, depending on the brand and also the rim width.