Check Out       > Welcome to Mountain Bikes London I am an adult - What size bike do I need? Adults bikes are generally measured by frame size (the measurement between the centre of the bottom bracket to the top of the seat tube). Riders Height Mainly Off Road Use Mainly On Road Use Road Racing Bikes In Feet & Inches Frame Size Required Frame Size Required Frame Size Required 4 feet 8 to 5 feet 0 12 to 14 inches 13 to 15 inches 46 to 48cm 5 feet 0 to 5 feet 4 14 to 16 inches 15 to 17 inches 48 to 50cm 5 feet 4 to 5 feet 8 16 to 18 inches 17 to 19 inches 50 to 52cm 5 feet 8 to 6 feet 0 18 to 20 inches 19 to 21 inches 52 to 56cm 6 feet 0 to 6 feet 2 20 to 22 inches 21 to 23 inches 56 to 60cm +   My child needs a bike - What size do they need? Children's bikes are generally measured by wheel size, rather than by frame size. Age of Child Wheel Size 2 to 3 Years 12 3 to 4 Years 14 4 to 5 Years 16 5 to 6 Years 18 6 to 9 Years 20 10 to 13 Years 24 29 Chapel Market, London, N1 9EN 4a Commercial St, London, E1 6LP 65 Woodgrange Rd, London, E7 0EL