PhotoShop 7 and above:
A feature that is really useful is the crop to size option. Enter the print size and resolution on the Options bar and then drag out a crop. This resamples the image to your exact size - the crop will always be proportional no matter how large or small the marquee is. This method eliminates the need to use the Image > Image size dialogue palette. You can save frequently used crop sizes (handy for wedding & social photographers). Click on the down arrow next to the crop tool (on the Options bar) and then click the small Create New Tool pre-set icon, enter a name and click OK. Your crop size is added to the list for future use. Cropping to Size Basic Steps:
1. Open Image
2. Select crop tool. The option bar has width & height fields. Enter the size you want followed by the unit of measurement (for example "in" for inches and "px" for pixels).
3. Now go to your photo and drag the cropping tool. It will be constrained to the sizes you entered.
4. You can reposition the crop by moving your cursor inside the border of the image and simply dragging it to a new location or you can use the arrow keys on your keyboard.
5. When you are happy with your selection, hit enter (Mac: Return). Note:
After you've enter an amount in the option fields they will remain until you clear them.