Saddles can be confusing, especially the fit. The first time someone says every horse needs a specific fit, it gets complicated. Why? Standards of measurement are sketchy, especially for the gullet.
Here’s what I’ve found helpful:
“Standard measurements for gullets described in Horseman’s Handbook of Western Saddles are:
Regular quarter horse bars: 5 3/4″
Semi-quarter horse bars: 6″
Full quarter horse bars: 6 1/4″ to 6 1/2″
Extra-wide quarter horse bars: 6 3/4″ to 7″
Arabian bars: 6 1/4″ to 6 3/4″ (has a flatter pitch than quarter horse bars)” quoted from: http://www.western-saddle-guide.com/saddle-gullet.html
And here’s a saddle guage that makes it easy to check your horse out: http://www.fteltd.co.uk/wow/nosaddlefitter.htm
For the front cinch, it should sit back from the front leg by about one hand width and be no more than one hand higher than your horse’s “elbow” point. The back cinch should be tight enough that they can’t get their hoof caught if they try to scratch their belly, but not tight like the front.
Now, remember, I’m not a saddle expert, and there are widely varying opinions. I recommend you seek out professionals when possible. This is a bit of helpful info I’ve found, and hope you find it useful!