Whilst irons sets can come in a choice of ten or more loft options, most players tend to have 7 or 8 irons in their iron set.
With hybrids offering more options then some iron sets these days maybe only have 5 or 6 irons, especially for junior, senior or women's custom fitting.
The key is to go through an iron custom fitting session to determine the distances you need to cover and how many irons you need. Then you go through wedge custom fitting to add short game clubs to finish off your set.
Many companies will offer you a standard iron set make up based on 5-iron to pitching wedge (PW), or possibly 4-iron to PW. They may custom fit you based on a shots taken with a 7-iron. However using 1 club to determine 6 or 7 other clubs may not create the optimum set for you.
At SGGT our Hogan Studio iron custom fitting uses a 4, 6, 8 and PW so you can try clubs right through the bag to see which ones fit your game.

Maybe your set could replace a 4-iron with a hybrid. Maybe you could blend different sets to have more forgiving irons in the longer clubs and more control clubs in the shorter irons. These can lead to very different set make ups from one golfer to the next.
As an example, over 20 fittings for irons, here are the set make-ups we created for our clients:
1 set of 4-PW
1 set of 4-PW with a different shaft in a 4-iron
4 sets of 4-PW with a different model of 4-iron to the rest of the set
2 sets of 5-PW with a 4 hybrid
5 sets of 5-PW
1 set of 5-9 with a 46° wedge
4 sets of 5-PW plus a Gap Wedge GW
1 set of 6-PW with a 4 & 5 hybrid
1 set of 7-PW with a 5 & 6 hybrid
So as you can see there is no standard set make up if you are correctly custom fitted. Find your perfect iron set make up by booking an iron fitting today.