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Fence Post Calculator

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Estimate concrete needed per fence post, including depth and hole diameter. Simple DIY post footing calculation.

Fence Post Concrete Calculator | Bags per Post

This fence post calculator estimates how many 25 kg concrete bags are required per post. Once activated, you will enter post spacing, hole diameter, and depth to determine concrete volume and bag requirements.

Fence Post Concrete Calculator

Units:
meters
meters between posts
centimeters
centimeters
For overdigging, bell-shaped holes, loss, etc.
Metric: m³ per bag (~0.02 m³ for 25 kg). Imperial: ft³ per bag (~0.6 ft³).

Enter fence length, spacing and hole size to estimate concrete.

This is an approximate estimate based on cylindrical post holes. Always check local frost depth and post size with your builder or supplier.

Related Calculators

Standard Post Hole Dimensions

General guideline:

  • Hole diameter: 2–3× post width
  • Depth: 1/3 of total post height (minimum)

Example:
Post height: 2.1m
Depth: 2.1 ÷ 3 ≈ 0.70m

Volume Example

Hole diameter: 300mm (0.3m)
Hole depth: 0.70m

Volume = π × (0.15²) × 0.70
≈ 0.049 m³ per post

Bag conversion:
1 m³ ≈ 1000L and 25kg bag covers ≈ 10L

0.049 m³ = 49L
49 ÷ 10 ≈ 5 bags per post

Concrete Mix Tip

Fast-setting post concrete is recommended for:

  • Fences
  • Mailboxes
  • Garden structures

Standard mix is fine but requires bracing and longer set time.

Frequently Asked Questions

How many bags per post on average?
Typically 3–6 bags depending on post size and depth.

Should I use gravel at the bottom?
A 100mm gravel base improves drainage.

Do posts need bracing?
Yes, brace during set time to avoid lean or shift.