First time poster here.
A few people here posted about gapping and I think those are pretty much in the range (some will say 12 yards and other will say 15). The reality is that unless you're a scratch (but actually maybe even better), your gapping can change from day-to-day. Pros don't hit their 7 iron 180 every single time, even they have shirt/long and right/left dispersions. I have fitted clubs and recently went for a gapping session to adjust any loft/lie issues. At the time of my gapping, I made very solid contact with each club (just had a good day that day) and then the following week, I wasn't hitting it as solid. Note: typically, any duffed shots should not count towards your gaping.
One thing to keep in mind is that when you do gapping, you should be using a launch monitor (and ideally, not range balls) to get the most accurate data. The other thing is that there will probably be some overlap in clubs meaning that your worst 7 iron (not a duff) can go 170 and your best 8 iron (not a thin shot) can go 175. Lastly, something to remember that though you may have some weird gapping in your irons, remember that your skill level will dictate how solid you hit the ball. Take what you have that day and roll with it. If you're 7 iron is going outside of 135-147 yards range, that's what you have that day and you need to make adjustments, don't force hitting that club because one day you hit it x distance.
EDIT: Just as a little side tip: when you make your decision on choosing which club to hit, err on the side of taking the longer club because most often people hit the ball short. If I was to give you an example for yourself: if you have 150 yards to the middle of the green (25 yard green), regardless of where the pin is you should be hitting your 6 iron, based on the number above. Rational: Assuming you won't duff your shot, your 6 iron dispersion is 148-160, with those numbers, you probably won't hit it past the green even with the roll (but that's also not bad based on stats) but most importantly, you shouldn't land it short of the green. You should never hit your 7 iron with hopes of hitting it flush and having some roll because at this point the front of the green is 137 yards, the odds are that you will mishit it somehow and will miss the green short.