Drupal Commerce Custom Sizes I am creating a Drupal Commerce website to sale Custom Stitched Thobes in which I need to get the Measurement from the customers. I am unable to understand where &amp; how should I add fields to take the measurements for the product he adds to cart.

Actually the idea is to offer some standard sizes like S,M,L or XL in case he don't want the standard sizes he can select Custom in Sizes Drop down, which will show up custom size text fields.

I was looking for a straight forward way to add text fields in Product Type through manage fields and check Enable this field to function as an attribute field on Add to Cart forms. so those fields can be appeared on add to cart form but unfortunately this option is not available for text fields.
Correct - the way the attributes system works, it requires you to define a SKU for every possible combination - depending on how many measurements options you have, it could be infinite. Instead you should look into line item fields that allow a customer to associate unstructured data with a product when it is added to the cart. This could accommodate both your fixed and variable sizes.