Men and women have different shoe sizes because their feet are structurally different, and most sizing systems account for this by using separate scales. The US system, which is the most obvious example, offsets women’s sizes by about 2 numbers: a women’s 9 is roughly equivalent to a men’s 7. But the difference goes deeper than just numbering. Men’s and women’s feet differ in width, arch shape, and overall proportions, which means the shoes themselves are built on different molds.
How Men’s and Women’s Feet Actually Differ
The size gap isn’t just about length. Men’s feet are wider, and that width difference is significant enough that foot breadth alone can predict a person’s sex with about 72.5% accuracy. In a study of foot dimensions, men had significantly greater foot length, foot breadth, and arch index measurements compared to women in both feet. Every major dimension of the foot, down to individual toe lengths in footprints, was measurably larger in men.
Proportions matter too. Women’s feet aren’t simply scaled-down versions of men’s feet. Relative to their overall foot length, women tend to have narrower heels, a higher arch, and a shorter distance from heel to the ball of the foot. This means a shoe designed around male proportions won’t fit a woman properly even if the length happens to be right. It’s like the difference between a tall, narrow rectangle and a shorter, wider one: same area, completely different shape.
Why the US System Uses Two Scales
The US sizing system assigns different numbers to men’s and women’s shoes, with women’s sizes running approximately 2 sizes higher than men’s for the same foot length. A woman who wears a size 9, for example, would wear roughly a men’s 7. This offset exists because the two scales were developed separately, each starting from a different baseline measurement.
Not every country does it this way. The European (Continental) system uses a single unisex scale based on the Paris point, which equals two-thirds of a centimeter. A size 42 is a size 42 regardless of gender. The formula is straightforward: multiply the length of the shoe’s internal mold (called a “last”) by 1.5. Because men’s feet are generally longer, they simply land higher on the same scale. The Mondopoint system, used widely in military and ski boot sizing, also works this way, measuring foot length and width in millimeters without separate gendered charts.
So the “different sizes” question has two answers. Biologically, men’s feet are larger and shaped differently. But the confusing numbering, where a women’s 8 and a men’s 8 aren’t the same shoe, is a quirk of the American and British sizing conventions rather than something dictated by anatomy.
Shoe Design Goes Beyond the Number
Shoe manufacturers use a solid form called a “last” to shape every shoe. Men’s and women’s lasts are built to different specifications, and research comparing women’s foot shapes to athletic shoe lasts found that the differences in width between lasts and actual feet can vary by up to 9 millimeters. Width grading (how much wider a shoe gets as it goes up in size) also tends to be larger in lasts than in real feet, by 3.5 to 5.9 mm per size step. This means that women at the extremes of the size range, very small or very large, are more likely to end up in poorly fitting shoes.
Width labeling adds another layer of confusion. A “B” width is standard (medium) for women but narrow for men. A “D” width is standard for men but wide for women. The letters are the same, but they represent different actual measurements depending on which side of the store you’re shopping on. If you’ve ever tried on a shoe from the opposite gender’s section and found it surprisingly tight or loose in the midfoot, this is why.
Why Fit Matters More Than Size
Getting the shape right, not just the length, has real consequences for comfort and injury risk. Women are more than twice as likely as men to develop patellofemoral pain syndrome (pain around the kneecap), and footwear design plays a role. Research on running biomechanics shows that women and men respond differently to changes in shoe characteristics. Women show greater variability in knee movement patterns when switching between different shoe types, possibly because differences in body proportions and muscle strength make their joints more sensitive to what’s on their feet.
Shoe design can meaningfully influence ankle movement during running, even if it doesn’t change what happens at the hip. This means a shoe that fits the length but ignores the proportional differences (narrower heel, different arch, wider forefoot relative to heel) can alter your gait in ways that accumulate over thousands of steps. Researchers have noted that many women’s athletic shoes are still designed by simply scaling down a men’s last rather than building from women’s foot scan data, and they’ve called for lasts that account for sex-specific proportions.
Shopping Across Gender Lines
If you’re buying shoes across gendered sizing, the conversion is simple in the US: subtract about 2 from a women’s size to get the men’s equivalent, or add 2 to go the other direction. A women’s 10 is close to a men’s 8. In European sizes, no conversion is needed since the scale is the same.
Keep in mind that length conversion doesn’t solve the width and shape issue. A man buying women’s running shoes in his converted size will likely find the heel too narrow and the forefoot too tight. A woman in men’s shoes may notice excess room in the heel and midfoot, leading to slipping. For casual shoes where precise fit is less critical, cross-shopping works fine. For athletic shoes or anything you’ll wear for hours on your feet, sticking with shoes designed for your foot shape will generally serve you better.