Whats the difference between mark up and margin?

and how do I calculate?

Margin
The percentage margin is the percentage of the final selling price that is profit.
Markup
A markup is what percentage of the cost price you add on to get the selling price.
i.e. 25% Margin means a bigger profit than 25% Mark Up because mark up is calculated before your overheads and other costs are paid whereas margin is calculated as pure profit after your overheads and other costs are paid.

If you buy an item for 拢1 and sell it for 拢1-50 your mark up is 50% your margin is 33.333%

Mark up is the amount you add to the cost of a product to arrive at its selling price. Margin is the different between the cost of the product and its selling price, so the two amounts are the same. However, the percentage difference is not the same. A product that is bought for $10 may be marked up $4 to sell for $14. The markup is 40 percent of cost. The margin is $4 which is 28.5 percent of selling price.

Now it is also possible to have an additional markup of $1 which raises the selling price to $15, and you can also have a markdown of $2 which brings the selling price down to $13. Markups, markdowns and additional markups and markdowns are typically measured in terms of dollars, whereas margin is typically measured in terms of percentage of selling price. Margin on a single product is not as meaningful as overall margin, that is, total revenue less cost of goods sold, converted to a percentage.

MARK UP MEANS AMOUNT EXPECTED FROM SALE
IT DEPENDS UPON BARGANING
MARGIN MEANS BELOW WHICH NO SELLER WILL SALETHE PRODUCT . IT'S A RESERVATION PRICE
MARGIN= COST OF PRODUCTION-SALE PRICE