It does - it also varies depending on how much sun you have. Dahlias are usually taller than usual for me due to only 6-7 hrs of full sun in my yard.
If you look at dahlia info on the various dealer's sites, you will notice some don't mention height, and some do, but not always the same on the various sites. I tend to assume a dahlia will be 4-5 foot - but this year I had a couple over 8ft. and a couple under 3 ft.
Not much help I know.
