Gross Margin is the Gross Profit as a percentage of Net Sales. The calculation of the Gross Profit is: Sales minus Cost of Goods Sold. The Cost of Goods Sold consists of the fixed and variable product costs, but it excludes all of the selling and administrative expenses.
Contribution Margin is Net Sales minus the variable product costs and the variable period expenses. The Contribution Margin Ratio is the Contribution Margin as a percentage of Net Sales.