While reading through all these posts, first let me say, thank you to all that have made lap quilts for people in wheelchairs. I can see why there are a lot of different sizes. If someone is just sitting in a chair, a larger size would be perfect, for a bed, a larger size perfect. For someone in a manual wheelchair that doesn't really move around, a larger one is perfect, but for anyone who is mobile, and moves around a lot, the 20X30 is perfect. This winter I even used a wall hanging that I made practicing a different pattern, and it covered my thighs, and a portion of my legs and it was great. Keep in mind that a lot of older people in wheel chairs don't have very big legs. So my opinion would be to make a bunch of 20x30 for more active people, and a little larger for non active. Then you've covered it all.