Question: how to calculate the percentage of cost of goods sold?
Answer: Find out your COGS (cost of goods sold). ... 
Find out your revenue (how much you sell these goods for, for example $50 ).
Calculate the gross profit by subtracting the cost from the revenue. ... 
Divide gross profit by revenue: $20 / $50 = 0.4 .
Express it as percentages: 0.4 * 100 = 40% .