I believe the minimum standard is sufficient. Test drive a sample with a foot that has been washed and see if there is slide to it. It is not just water but the residual soap that can make our feel slide.

I do not believe the myth that grout lines provide enough friction, ever, and certainly not in a 4x4 tile. I have 3/4" hex tiles on my bathroom floor. Many would say the grout is enough to make them viable. Wrong. I have ice skated on that floor many times.

My dad is an engineer. The grout myth is one of his pet peeves. The apple doesn't fall far.

I would never use a highly polished tile on the floor in a bathroom, not matter what they claim the DCOF is.

Thanks for the replies!! I will not use the polished hex. And thanks to @Kendrahs dad!

Do you think the 12 x 24 satin minimum standard floor tile is sufficient? Or is that a use test?

If you are shopping at a good local independently owned tile shop they will let you borrow the 12x24 sample tile. Take it home and test it. You can even place it on your shower floor and test while wet/soapy.

I have matte 1.5" x 1.5" mosaic on my shower floor and even that can be slick if you had to make a sudden move right after you rinsed conditioner from your hair.

oh boy, @chispa. It's looking like those gorgeous Italian tiles are not going to be a viable option... Thanks for weighing in.

Any tile ( just about ) will be slick if it is wet and soapy. The main floor of your bathroom should not be soaked with water or soap ( if it is, then you have bigger problems ) . We use matte finished 12 x 24 floor tiles on bathroom floors all the time with no issue.

We strongly urge every one of our customers to add a grab into the tub/shower area ( they are not institutional or ugly these days ) because anyone at any age can slip in the shower.

Good luck

Grab bar is a great idea, @Debbi Washburn. It was not on my list, thanks for the suggestion!

Good to know! Many thanks @chispa!

Would certainly suggest that you go above the minimum especially if an older person will be using the shower. Wouldn't count on grout lines providing enough friction to prevent slipping.

Thanks so much @Norwood Architects. I just picked up different samples that have some texture, from what I'm hearing here it is better be same than sorry. Thanks for weighing in.