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Post Hole Concrete Calculator

Bags of concrete per fence or deck post, with the volume of the post subtracted. Enter the hole diameter and depth in inches, pick the post, and set the number of holes.

What are you pouring?
Units

Fence or deck post holes

The post is subtracted. Gravel (optional) is left out of the concrete.

Bag size
Add your prices (optional)

Use your supplier's prices. We don't show average prices because they vary too much by area.

Concrete needed

1.01 cubic feet

0.038 yd³ · 0.029 m³ · includes 10% extra

You need about 1.01 cubic feet of concrete, or 2 bags of 80 lb mix.

Bags of premix

  • 440 lb bags
  • 350 lb bags
  • 360 lb bags
  • 280 lb bags
  • Before extra0.03 yd³ (0.9 ft³)
  • Weight of bags160 lb
  • Per hole1.01 ft³ · 2 × 80 lb
  • Ready-mix costAdd a price per yd³
  • Bagged costAdd a price per bag

One 80 lb bag makes about 0.60 ft³ (manufacturer's published yield). Bags are rounded up.

Bagged mix makes sense at 0.04 yd³. A ready-mix truck for a load this small would usually come with a minimum-order or short-load charge.

Estimate only, not a quote or engineering advice. Disclaimer

How much concrete per post

Bags per hole, post subtracted, no waste added
Post, hole diameter × depthft³50-lb60-lb80-lb
4×4, 8 × 24 in0.53221
4×4, 10 × 24 in0.92332
4×4, 10 × 30 in1.15432
4×4, 12 × 36 in2.10654
6×6, 12 × 36 in1.73543
6×6, 16 × 42 in4.1512107

Bags are rounded up per hole here. For a whole fence, the calculator totals the volume first and rounds once, so it may need a bag or two fewer than this table times the number of posts.

How the calculation works

Concrete per hole = (π × (hole diameter ÷ 2)² − post area) × (hole depth − gravel)

Square posts use their actual size: a 4×4 is 3.5 × 3.5 in and a 6×6 is 5.5 × 5.5 in. If you put gravel in the bottom of the hole for drainage, enter its depth and it is left out of the concrete.

Hole size

QUIKRETE's directions for setting fence posts call for a hole about 3 times the post's width and about one-third of the post's overall length deep. For a 4×4 that works out to roughly a 10 to 12-inch hole. Deck footings, frost depth and fence height can call for more, so check local rules for anything that carries a structure.

Dedicated tables: concrete for a 4×4 post and concrete for a 6×6 post.

Frequently asked questions

How much concrete per fence post?

A 10-inch hole 24 inches deep with a 4×4 post takes 0.92 ft³ of concrete: 3 bags of 50-lb mix, 3 bags of 60-lb mix or 2 bags of 80-lb mix.

How many bags of concrete per fence post?

With a 4×4 post in an 8 to 10-inch hole 2 ft deep, expect 2 to 3 bags of 50 or 60-lb mix, or 1 to 2 bags of 80-lb mix, per post. Wider or deeper holes and 6×6 posts take more; use the calculator with your hole size.

Should I subtract the post from the hole?

Yes, that is what this calculator does. A 4×4 post 2 ft deep displaces about 0.17 ft³, almost half of a 50-lb bag per hole, which adds up over a long fence.

Can I use fast-setting concrete?

Yes. Fast-setting mixes are sold for fence posts and often come in 50-lb bags. Yield varies by product, so check the bag; the calculator uses standard concrete mix yields.

Related

Sources