Use the dimensions calculated on this page to place an order with this file and maintain its proper aspect ratio. This page helps you calculate the dimension you need to use in one direction when you know what’s needed in the other direction.
For example, if you know you need your image to be 18” wide, but don’t know what that sizes to in height, the calculator above will calculate that for you. You can then use those results to start your order and maintain your full image.