Slant Height of a Cone Calculator l = √(r² + h²). Radius Height Slant height 9.487 Step-by-step with your numbers: 1. Values used: 2. Radius = 3 3. Height = 9 4. Slant height = 9.487 Did we solve your problem today? 👍 Yes 👎 No Thanks for the feedback! Hypotenuse of radius and height. FAQ Use? For surface area: πr(r+l). Related calculators Cone Calculator Find a cone's volume, slant height and surface area. Pythagorean Theorem Calculator Find the hypotenuse of a right triangle from the two legs. Surface Area of a Cone Calculator SA = πr(r + l).