What percentage is keystone mark-up?

Keystone mark-up means setting the sales price of your product double the price it costs you. It is equally advantageous and disadvantageous depending on the condition. Suppose the keystone mark-up is 50% of its initial cost. It indicates that if the product's cost is $100, you set the sales price to $200 and earn a profit of $100, making the 50% of $200.