Easily determine your new belt size requirement by measuring a belt you currently wear. Lay your belt down flat and place a tape measure at the end of the buckle and measure to the hole you currently use. Round up to the nearest available size. IE 35 inches = size 36 belt.
Do not base the size on your pant size or current belt size label. As styles change so can sizing and labelling. Remember to choose the belt for the pants you will most often be wearing. For example some denim is worn around the hips vs the waist meaning 2 sizes up from your waist size.
Investing in a high quality belt makes good fashion sense and proper belt sizing is equally critical.
Wrap a narrow piece of paper approximately 1 cm wide around your wrist and make sure it is comfortable and not snug. Measure the length of the piece to the nearest CM and round up. ie wrist is 17.5 CM order 18 CM Leather will soften and your bracelet will loosen over time.