What size bar mitts you have. Do you just match up
your glove size. Ie. Med for Med gloves.
do bar mitts come in sizes? my gloves I just buy for my hands. I can wiggle the big gloves into the bar mitts but I usually use smaller thinner gloves w/ the mitts. it's a delicate balance, just warm enough not to sweat. my hands warm as I ride so I sometimes bring a 2nd pair of gloves with me that are lighter & change 1/2 way thru my ride
I guess these are called "middle" & I could see using larger ones on the MTB
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I guess for the drop bars I got large
https://www.amazon.com/gp/product/B0...TF8&th=1&psc=1
but they both seem just right