There are a few different ways that you can measure legroom and headroom in a vehicle. The most common way is to use a tape measure. You will want to measure from the floor of the vehicle to the top of the headliner. This will give you an accurate measurement of how much space you have to work with.
Another way to measure legroom and headroom is by sitting in the vehicle and measuring from your head to your feet. This method is not as accurate, but it will give you a general idea of how much space you have to work with.
The last way to measure legroom and headroom is by using your own body measurements. To do this, you will need to know your height and weight. Once you have these numbers, you can plug them into a online calculator that will tell you how much space you need in a vehicle based on your body size.