Conifers are pretty fast growing but the growth rate depends on the type of Conifer as some Conifers are faster growing than others.
If you get a slow growing Conifer it will grow up to 12 inches or 1 foot tall per year while faster growing Conifers can grow up to 24 inches or 2 feet per year.
When you buy a Conifer it should have a tag stating how fast that type of Conifer will grow each year.
Still they're very fast growing as long as you properly care for them.