Same profit, two percentages
The profit is the same number, but it is divided by different bases. So margin is always lower than markup and never reaches 100%, while markup can be 300% or more.
Converting between them
Margin = markup / (100 + markup) × 100; markup = margin / (100 − margin) × 100. A 25% markup is a 20% margin, a 50% margin is a 100% markup.
Pricing for a target margin
Price = cost / (1 − margin/100). For a 30% margin on a cost of 700 the price must be 700 / 0.7 = 1,000. Adding a 30% markup instead gives 910 and only a 23% margin.