Cat Shelf Size Calculator: Step and Lookout Sizes from Your Cat

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Opens on the book's own cat and wall. Change any number to your own and press Calculate.

Your cat's weight the heaviest cat that will use it

Weight in

Head and body nose to the base of the tail

Lengths in

Or weigh by difference (optional)

You alone on the bathroom scale

You holding the cat the same scale, same units

The board and the wall

Board depth 1x12 = 285.75 mm (11¼ in)

Stud spacing center to center; 16 in = 406.4 mm

Board past each bracket 1 in = 25.4 mm

Landing check × the weight

Enter your cat and press Calculate.

The formula

Weight in newtons = kg × 9.81. Pounds = kg × 2.2046
A step = head and body × 1; a lookout = head and body × 2
A board on two studs = stud spacing + 2 × the overhang; on three studs = 2 × spacing + 2 × overhang
Area = length × depth; ft² = m² × 10.764 (never × 3.28)

The book's worked example, Chapter 1. The book's design cat weighs 6 kg (13.23 lb), which is 58.86 N, and is 460 mm (18.11 in) from nose to tail base. An 18 in (457.2 mm) step on two studs is 2.8 mm short of one cat; a 34 in (863.6 mm) lookout on three studs is 56.4 mm short of two. On a 1x12 they are 0.13064 m² and 0.24677 m² (1.406 and 2.656 ft²).

Measure a sleeping cat, nose to the base of the tail, and leave the tail out. Weigh yourself, then yourself holding the cat, and take the difference. Metric first, imperial beside it. Prices are illustrative US home-center prices from November 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.