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Slant Height Calculator.

Calculate the slant height from a base radius and perpendicular height.

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Set your values

Results update as you type.

Result: slantHeight: 5.00000000

Result

slantHeight: 5.00000000

Use Cases

Construction and DIY Projects

Determine the slant height for building cone-shaped structures, roofs, or decorative items. Helps in cutting materials accurately.

Example: A cone with radius 3 ft and height 4 ft has a slant height of 5 ft.

Geometry Homework and Exams

Quickly verify slant height calculations for math assignments or test preparation, saving time and reducing errors.

Example: Check your answer for a cone with radius 5 cm and height 12 cm.

Frequently Asked Questions

What is slant height and how is it calculated?
Slant height is the distance along the lateral surface from the base edge to the apex. For a right circular cone, it's the square root of (radius squared plus height squared). Enter the base radius and height, and the calculator gives the slant height.
Can I use this calculator for a pyramid?
Yes, if the pyramid has a regular base and you know the apothem (or half the base width) as the 'base radius' and the vertical height, the slant height is the same formula: sqrt(radius^2 + height^2).
What units does the calculator use?
The calculator accepts any consistent units for radius and height (e.g., inches, cm, meters). The slant height will be in the same unit. Ensure both inputs use the same unit for accurate results.

Tips & Common Mistakes

Tips

  • Ensure both radius and height are in the same units before calculating.
  • For a cone, the slant height is always greater than the height and radius individually.
  • Use the Pythagorean theorem: slant height = sqrt(radius^2 + height^2).
  • Double-check your inputs for typos, as small errors can significantly affect the result.

Common Mistakes to Avoid

  • Using diameter instead of radius. The calculator expects the base radius, not the diameter.
  • Mixing units (e.g., radius in inches and height in feet) without converting, leading to incorrect results.
  • Forgetting to square the inputs before adding, or taking the square root incorrectly.

Last updated: August 13, 2026