Perimeter of a Rectangle Calculator P = 2(L+W). Length Width Perimeter 26 Step-by-step with your numbers: 1. Values used: 2. Length = 8 3. Width = 5 4. Perimeter = 26 Did we solve your problem today? 👍 Yes 👎 No Thanks for the feedback! Rectangle perimeter. FAQ Square? P = 4a. Related calculators Rectangle Area Calculator Find the area and perimeter of a rectangle. Perimeter of a Square Calculator P = 4a. Perimeter Calculator Rectangle perimeter.