On the bath towel, I think 2.5 or 2.75 inches is enough. You can stitch much larger, but don't enlarge a font or you will wind up with long stitches that will pull and snag. Hand, slightly smaller. Face, maybe just the initial of the last name. Kitchen towel - size will depend on whether you are adding a design as well, and what size the design is. If towel will be folded in 1/3's, you need to contain the stitching to the center one-third, with some space to the sides. So, it's more about the total width than the height. You'll get several different opinions on this!

I agree totally with graceandham about placement and size. I also like to monogram on a nice piece of fabric and then applique onto the towel. This way very few stitches on back. Welcome to Cute, glad to have you with us/Lillian

Use the same thread in the bobbin so that it will look nice from the back too.

Thank guys I will try it and let you know how I get on. And what stabiliser should I use front and back? Thank you for your help

For the bath towel I like to choose a design that I can remove elements from to then use it on the hand towel.
I keep the text the same size text on both the bath towel and hand towel.
For the face washers I leave the text off and use a segment of the design, or leave the design off and just use the initials.
It all comes down to the design you choose and your own personal preference.

I will often do a print out of the designs (100% size) and place them on the articles before I make a decision, certainly avoids the heartache of choosing the wrong design or stitching the design in the wrong place.
hugs n roses, Meganne