An outseam measurement is a measurement of the length of the leg of pants or trousers from the upper edge of the waistband to the bottom hem of the leg. This measurement can be taken by laying the pants on a flat surface and taking the outseam measurement from the waist of the pants following the side pant seam to the bottom of the leg. Someone can also follow the same measurement procedure but with the pants on.
A measuring tape is the most important tool needed for this project. However, someone else is needed to take the measurements if they are to be taken when the pants are on. Otherwise, it can be done by one person.
If one is taking the measurements when the pants are on and for the purpose of sewing new pants, one should place the measuring tape at the upper edge of the waistband and measure down to the ankle. This should be done for both legs, and the results should be recorded. Sometimes, the measurements of the right leg and that of the left leg may differ with half an inch or more, but this is normal. Another measurement should be taken from the top of the waistband up to where the pants should be hemmed, and the measurement should be recorded.