Standard bottle size is 750 ml, which is 25.36 ounces. If I find a that any place charges more than 4x the bottle price for their standard pour, I'm going to go elsewhere or maybe have a beer.
Example - Knob Creek is common pour at most bars around town. I know I can buy a bottle of Knob Creek for $25. If a pour is 2oz, then that bar will pour 12 drinks per bottle. Using 4x rule, Knob Creek is a $100 bottle/12 = $8.33. If pour is only 1.25oz, then $100/20 = $5.
I know restaurants and bars need a mark up to stay in business. 4X cost is a very high gross margin. What I find is that chain type places are the worst for pour to price. Example, my local Chili's uses an exact pour of 1.25oz and they never vary this. They charge $7 for Knob creek, so I'm not buying.
I recently went to a cigar bar that had a very good selection of whiskey. I had a Thomas Handy Rye and it looked expensive on menu; $14. But, the pour was a good 3ozs. Using the same 4x rule, Handy goes for $55, so $220/8 pours/per bottle at 3+oz = $27.50. So, that was a very fair price.