Construction Post Length Calculator

Find the right post length for ground, footings, and caps today easily. Adjust bury depth, slope, and waste, then download your report CSV PDF.

Calculator

Height above finished grade.
Below grade to post bottom.
Concrete below the post, if used.
Drainage layer under the post.
Extra length above target finish height.
Add for low-side posts on sloping sites.
Allowance for squaring ends and final cut.
Choose a percentage or a fixed extra length.
%
Used when waste mode is percent.
Used when waste mode is fixed length.
Controls displayed results and exports.
Rounding for on-screen values.

Example data table

Scenario Exposed Embedment Footing Gravel Top allowance Waste Required length
Deck corner post 6 ft 3 ft 8 in 4 in 1.5 in 5% ≈ 9.99 ft
Fence line post 5 ft 2.5 ft 0 in 3 in 1 in 4 in ≈ 7.92 ft
Pergola support 2.4 m 0.9 m 0.2 m 0.1 m 0.03 m 3% ≈ 3.75 m

Examples are illustrative; verify local requirements and site conditions.

Formula used

Subtotal length adds all required segments:

  • Subtotal = Exposed height + Embedment depth + Footing thickness + Gravel thickness + Top allowance + Grade adjustment + Trim allowance

Waste allowance is applied as either:

  • Waste = Subtotal × (Waste% / 100)
  • Waste = Fixed extra length

Required post length is:

  • Required = Subtotal + Waste

How to use this calculator

  1. Enter the exposed height you want above finished grade.
  2. Enter embedment depth to the post bottom below grade.
  3. Add footing and gravel layers if your detail includes them.
  4. Include top allowance for caps, brackets, or trimming later.
  5. Add grade adjustment for posts on the low side of a slope.
  6. Select a waste method: percent for variability, or a fixed length.
  7. Choose output unit and rounding, then press Calculate.
  8. Use Download buttons to export your latest result.

Measure carefully, verify codes, and build posts that last.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.