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Seat-to-Floor Height: There is no set rule for seat-to-floor height. It is based on personal preference. However, it is important to make sure you have enough ground clearance so your footrests don't drag the ground.
While seated, measure the distance from the base of the heel to the bend in your knee. Add the desired clearance from the bottom of the footplate to the ground at least 2 inches. Add these two measurements together and you have your minimum seat-to-floor height.