Do you know how much you spend per month on rent, employee wages, and other fixed expenses? The most practical way is to add up all those monthly costs, divide by the approximate number of shirts you sell in a month, and add that to the cost of the shirt (R$ 15) plus the profit margin you want. For example, if your expenses come to R$ 3,000 per month and you sell around 200 shirts, you add about R$ 15 in expenses per piece, totaling R$ 30, and then you add a 30-50% profit margin depending on what your local market allows, landing somewhere between R$ 39 and R$ 45. The important thing is not to let just the cost of the piece guide the price - there are other numbers involved in all this.