The size of snowshoe you need depends on your body weight, the weight of your gear, snow type, and whether you snowshoe on broken-out trails or travel cross-country, on fresh powder.
But if you are about to buy a new pair of snowshoes, don’t take manufacturer’s size recommendations as gospel. Their snowshoe fit guides tend to put you into a snowshoe that is too big and much heavier than you need. The last thing you want is to carry more weight in winter than necessary, or get stuck with a giant pair of snowshoes that are impossible to maneuver with. I’ve done this myself, and it’s money down the drain.
Generally, the larger the snowshoe, the more flotation and decking surface area it will provide. If you plan on snowshoeing on powder and breaking trail more than 80% of the time, then I’d recommend you get a larger snowshoe with a lot of flotation. However, if you plan on snowshoeing on broken-out trails or a mix of snow and icy, rocky terrain then I recommend that you downsize a level. You don’t need the flotation, and you’ll find it difficult to maneuver with 30″ snowshoes on narrow, trench-like trails.
Snowshoes for Rocky Terrain
Let me give you a real-world example. I live in rocky New England. I mainly hike on mountain trails under tree cover, with moderate snow levels. I avoid snowshoeing on trails that are not broken out and mainly hike on older, crusty snow or a dusting of powder. I weigh 180 lbs and carry a 20-30 lb pack on winter day hikes and backpacking trips.
At one point, I used 30″ Atlas Snowshoes and then 30″ Northern Lite ultralight snowshoes. Both proved too large for practical use because they were too wide to fit in the narrow trench of a broken-out trail and they were difficult to turn around in while wearing. Using them was downright unpleasant, so I downsized to 25″ MSR Lightning Ascent snowshoes. That has proven to be a good switch.
If you add my weight and gear weight together, it comes to 210 lbs on the high end when I’m backpacking and 200 lbs on the low when I’m day tripping. That puts me into the 30″ Lightning Ascent if I were to follow the MSR fit guide, which doesn’t work for New England snowshoeing.
Most fit guides from snowshoe manufacturers tend to put you into a snowshoe size designed for powdery snow requiring a high degree of flotation. If you plan on snowshoeing on packed trails, consider downsizing to a shorter and narrower snowshoe, than the one recommended for your combined body and gear weight.
If in doubt, ask around. Post a question about sizing on an online forum or facebook group with local hikers that are familiar with the terrain in your area. They can give you the advice you need to purchase the right size snowshoe for your needs.