I'm a little confused regarding bike sizing for different models.I'm helping to search for a bike for a lady friend and am wondering if the mixte is measured the same way as a male oriented bike.i seee mixtes offered in 50cm and 20 inches.Is that the same as a road bike with a top tube?My mountain bike is 17 inches and it fits great but on a road bike i take a 54cm or 56 cm.Can someone clarify/

To the extent that sizing convention even exist anymore, MTB sizing is typically in inches and road bike sizing is typically in centimeters and refer to the length of the seat tube, sometimes actual, sometimes virtual, with MTBs typically being shorter. 17' MTB and 54cm road would both be considered a "medium" sized bike. With all the variation in sizing conventions, I usually look at effective top tube length first when choosing a size.

So mixtes are measured the same as road bikes?

Some are. Do you have specific examples?

The SOMA Buena Vista is sized like road bikes.
https://www.somafab.com/archives/prod...a#tabs-588-0-3

MTB's and road bikes are built differently with MTB's having a longer top tube as the norm for frame size. I ride a 51cm Road bike that equates to 20. A 20" MTB is a lot bigger than I could handle. I ride a 15" one but in different manufacturers could ride an 18" and it would fit perfectly.

How a Mixte frame fits in I could not say but womans road frames do have a shorter top tube for Frame size and I believe the MTB's are the same.

Mixte does not equal woman's frame.

+1 Mixte sized just like road bikes. I have had several, I've got three right now.

Back in the olden days, we had something called a horizontal top tube, and bicycle sizing was fairly simple, you sat on the bike, if your privates cleared the top tube, feet flat on the ground, the frame was the right size, you adjusted the saddle so there was a fist full of seat post, and you were done. For a Mixte or a Ladies frame, all the dimensions were the same with the exception of the top tube. In other word if you took a men's frame and a ladies frame at set one on top of the other, they would be the same size. This all changed with the invention of the sloping top tube, because they tossed the rules of sizing out the window. Some bicycles were measured from the actual new location of the top tube, others were measured from where a horizontal top tube would be, if there was one. The seat tube never was a good place to measure, because seat height is not dependant on it, and different manufacturers use different ratios of top tube length to seat tube length. We need a new bicycle measuring system, that is well documented.

Mixte does not equal woman's frame.

Here's a generic size calculator. https://www.ebicycles.com/bicycle-tools/frame-sizer

That's why I said a Mixte or a Ladies frame, while not equal they can be functionally equivalent, in that there is no big honkin' top tube to try and step over. Mind you in many parts of the world, the term step through frame actually fits better, because both men and women ride that style all the time, especially older fellows who might have trouble lifting their leg over the top tube. The only reason they aren't more popular in North America among older men is that many older guys have this fear that if they rode on a "girls bike" even once, they would turn gay.

That explains it!!!