Choosing Snowshoes
Snowshoes today are divided into three types:

• Aerobic/running - small and light; not intended for backcountry use
• Recreational - a bit larger; meant for use in gentle to moderate walks of 3-5 miles (5-8 km) at a time
• Mountaineering - the largest; meant for serious hill-climbing, long-distance trips and off-trail use

Sizes are often given in inches, even though snowshoes are nowhere near perfectly rectangular. Mountaineering shoes can be at least 30 inches (76 cm) long by 10 inches (25 cm) wide; a lighter pair of racing shoes can be slightly narrower and 25 inches (64 cm) or shorter.
Full Article