Perimeter Calculator Rectangle perimeter. 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! P = 2(L + W). FAQ Other shapes? Use the shape-specific calculators. Related calculators Rectangle Area Calculator Find the area and perimeter of a rectangle. Square Calculator Find a square's area, perimeter and diagonal.