Here is how I go about it. I don't show a markup on the garment per say. I show it on invoicing as the price I get it at plus shipping and tell my clients that. I have and continue to time everything I do from start to finish. I do not get into a rush because let's face it; no one gets into a rush 100% of the time unless they are crazy, psycho, and a gluten for punishment to burn out early in life. I base it on the need of someone being hired in any future time period, insurance cost for employee benefits and perks. All over head due to building, materials, and so on. Only you know what yours is.
Then I take all my equipment and calculate it all as what it cost to buy it, divide that into 7 years as legal write off for depreciation. and get my machine cost per hour, man hours per hour and so on.... you get my drift. Then I add all my hourly costs up and divide that into how much I can produce per hour and then mark that up by 50%. If you do this you are making what you would need to pay all the overhead...given that you have the business rolling in that is...plus have money to upgrade things, fix things, and grow the business later down the road.
Hope this helps you all in your business endeavors!