What size boots would I wear if I wear 7.5s in sandles?

When you ride you will be wearing two pair of socks minimum. Most people wear a sport sock and then a thick motocross sock. If you wear a 7.5 shoe, you should go at least one to two shoe sizes bigger for the boot. Now, my daughter and my son both wear boots that are two sizes larger than their shoe size. I wear boots that are one size larger than my shoe size. My children do not like a snug fitting boot, I do. Some boots do not come in half sizes. in that case go to the next larger size. So, if you like your boots to be snug/tight, go with one size larger. If you like a little room in your boot, then go two sizes larger. Don't forget to look at used boots - men or women's boots (it is dirt biking, they are going to end up getting tore up and dirty anyway). I have picked up used boots at yard sales and Ebay in the past.

Good question Megan. When you wear Motocross boots you usually wear thick socks as well. I would show some interest at a bike shop that sells the boots till you see what fits you in size, note their price then hit your computer for what is online.