Your “real inseam” -- or inside leg length -- is the distance between your body where it sits on your bike saddle and the ground.
This will typically be an inch or two longer than the length of your trousers, but you’ll want to measure to be sure.
You’ll use this number on the chart to get a feel for how the different models will fit you.
Gather the tools needed:
Wearing your regular riding shoes and with your back to the wall, stand with your feet spread so there is about 7 inches between them - this is about the distance apart your feet would be when straddling a bike with your feet on the ground (standover height).
Place a hardcover book against the wall with the spine of the book facing upward. Slide the book upwards towards your groin until it is solidly against your body. This may be a bit awkward, but is way more comfortable -- and safer! -- than trying to ride a bike that is too big.
If you have a buddy helping you, get them to measure from the floor to the top of the book spine while you hold the book in place. If you’re going it alone, carefully hold the book in place and measure from the ground to the top of the book spine.