Use this calculator to see what a markup produces as gross margin, or what selling price is required to hit a target gross margin.
If a job costs $10,000 and you add a 50% markup, the selling price is $15,000. The gross profit is $5,000, but the gross margin is only 33.3% because margin is profit divided by selling price.
To achieve a 50% gross margin on a $10,000 job cost, the selling price would need to be $20,000.