Sisal Rope Calculator: Turns and Rope for a Scratching Post

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

Start from fills the boxes below

Post

Side, or diameter mm; a 4x4 is 88.9

Post height mm; 36 in = 914.4

Left bare at the foot mm

Rope

Buying the rope

Other rope from the same coil m, e.g. the bridge

Coil length ft

Would it stand on its own?

Post, foot and rope weigh kg; the book's post, worked out in Chapter 8

Half the base mm, center to the edge it tips over

Top of the post mm above the floor

Cat's weight kg

Enter the post and press Calculate.

The formula

Turns = wrapped height ÷ rope diameter, rounded up (each turn sits tight on the one below)
One turn, square post: 4 × side + π × rope diameter (four quarter-circles round the corners)
One turn, round post: π × (post diameter + rope diameter)
Push that tips a freestanding post = its weight × half the base ÷ the height of the push

The book's worked example, Chapter 8. The book wraps the top 800 mm of a 914.4 mm 4x4: 800 ÷ 12.7 = 62.99, so 63 turns of 395.5 mm: 24.92 m of ½ in sisal. With the bridge's 3.6 m, that is 28.52 m (93.57 ft) from one 100 ft coil, with 1.96 m to spare.

Staple the rope's ends into the post and glue as you go. The book stands its post on an 18 in foot and fixes it to a stud with a small bracket at the top: on its own it would tip under a push of about a third of the cat's weight. 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.