Ruthie, I have a bunch of these all from Hawaii. The long ones are approx. 56" x 45" and they go to the ankle. The short ones are approx. 67" x 23" and go to the knee (I have no idea why they are wider!). These are the ones I wear the most for poolside. I even swim in them (I have thigh issues!

). These are all in a light rayon batik. I have one from Mexico that is a heavier cotton, it's 64" x 34". These are all basic rectangles with fringes on the shorter ends. I think one and a half times the hip measurement x length you desire is plenty for a basic side tie style.
I have made a couple from cotton prints that I wear as wrap skirts. I measure twice the hip circumference and then from the waist to whatever length you want the skirt to be. When cutting, I add a tie tab - that is, from the waist add an extra 12" to 18" for ties then cut down about 3", in at an angle to the double measured hip measurement and down to the hem, curving if desired for a nice look when worn. On each side. So you wrap around twice and tie with the tab ends. Harder to describe than it is to do. I can draw it on paper and scan for you if you want, but the basic rectangles are the easiest for holiday wear.
How fun! Have a great holiday!