How Much Concrete Do I Need per Fence Post?

Plan on about 3 bags (50 lb) of fast-setting concrete per 4 × 4 post on a 6 ft fence, using Quikrete’s hole size. A 6 × 6 post needs about 6.

Updated October 7, 2026

Quikrete’s Rules for Post Holes

• Width: three times the post’s width.
• Depth: one-third to one-half of the post’s height above ground, plus 6 in.
• Base: 6 in of gravel or crushed stone in the bottom.
• Fill: concrete to 3–4 in below the ground. Top with soil or slope the concrete to shed water.

A 50 lb bag of Quikrete Fast-Setting Concrete yields about 0.375 cu ft. Quikrete’s own example is two bags for a 3 in post in a 9 in × 30 in hole.

Bags per Post

The table assumes holes at the minimum depth (one-third of the height plus 6 in), 6 in of gravel, and concrete to 3 in below grade:

Deeper holes, at half the height plus 6 in, take proportionally more. Holes always end up a bit irregular, so buy a few extra bags.

Before You Dig

Call 811 a few days ahead to have buried utility lines marked. Check your area’s frost depth and any local fence rules; posts set above the frost line can heave. The fence calculator adds up posts, concrete, gravel, rails, and pickets for your whole fence.