How deep should a post be for a 6 foot fence?

24 inches, a third of the height, in a hole about 10 inches across for a 4x4. The post is 8 ft long, so buy 8 ft posts, and each hole takes 1.01 cubic feet of concrete: 2 bags of 80 lb or 3 of the 50 lb fast-setting mix.

How deep for an 8 foot fence?

32 inches by the one-third rule, so the post needs 10.7 ft and you buy 12 ft posts. An 8 ft fence catches a lot of wind: use 6x6 posts at 6 ft centres, a 16 in hole, and 6 bags of 80 lb per post.

Is 2 feet deep enough for a fence post?

Yes for fences up to 6 ft in ground that does not freeze deeply, which is why 24 inches is the minimum here even for a 3 or 4 ft fence (a 4 ft picket fence still gets a 24 in hole and 6 ft posts). Go deeper for taller fences, gate and corner posts, sandy soil, and wherever the frost line is below 2 ft.

What is the frost line and why does it matter?

The depth to which the ground freezes in winter. Water in the soil expands as it freezes and lifts anything sitting above that depth, so a post footing that stops above the frost line is heaved a little every year until the fence leans. In the northern United States and Canada the frost line is 3 to 4 ft or more; the local building department publishes the figure and the code depth for posts.

How wide should the hole be?

About three times the width of the post: 10 in for a 4x4 (which is 3 1/2 in), 16 in for a 6x6. A wider hole means more concrete but a footing that resists leaning; a hole barely bigger than the post leaves too thin a collar of concrete to do anything.

Do fence posts need concrete?

Not always. Line posts in firm, well-drained soil can be set in compacted gravel, which drains and is easier to replace. Corner, end and gate posts, posts in soft or wet ground, and any fence over 5 ft should be concreted. In either case put 4 to 6 in of gravel in the bottom of the hole so the end grain is not standing in water, and crown the concrete so rain runs off the post.

How deep should a fence post be? (by fence height)

Set a third of the fence height in the ground and never less than 24 inches: 24 in for a 6 ft fence, 32 in for 8 ft, and the 24 in minimum for anything 6 ft and under. That makes a 6 ft fence an 8 ft post in a 10 in hole with 2 bags of 80 lb concrete. Where the ground freezes the hole must reach below the frost line, which can be deeper than the rule.

Open the fence calculator

Depth, post length and concrete by fence height

The rule is a third of the height above ground, with 24 inches as the floor. Post length is height plus depth, rounded up to the 2 ft steps posts are sold in. Concrete is the hole minus the post plus 10%, in the three bag sizes; the fence calculator does the same for any height, hole and bag.

4x4 posts (3 1/2 in actual), 10 in hole
Fence height	Depth	Post needs	Buy	Concrete per hole	80 lb bags	60 lb bags	50 lb bags
3 ft	24 in	5 ft	6 ft	1.01 cu ft	2	3	3
4 ft	24 in	6 ft	6 ft	1.01 cu ft	2	3	3
5 ft	24 in	7 ft	8 ft	1.01 cu ft	2	3	3
6 ft	24 in	8 ft	8 ft	1.01 cu ft	2	3	3
8 ft	32 in	10.7 ft	12 ft	1.35 cu ft	3	4	4

6x6 posts (5 1/2 in actual), 16 in hole, for tall fences and gates
Fence height	Depth	Post needs	Buy	Concrete per hole	80 lb bags	60 lb bags	50 lb bags
6 ft	24 in	8 ft	8 ft	2.61 cu ft	5	6	7
8 ft	32 in	10.7 ft	12 ft	3.48 cu ft	6	8	10

When the rule is not enough

Frost. The bottom of the concrete must sit below the frost line, or the footing is lifted a little every winter. In cold regions that is 3 to 4 ft even for a 4 ft fence; the local code sets it.
Wind and height. An 8 ft privacy fence is a sail. Deeper holes, 6x6 posts and 6 ft spacing all help; the posts guide shows what the closer spacing adds.
Gates and corners. A gate post carries a swinging load on one side; set it 6 in deeper than the line posts and use a 6x6 for anything over 4 ft wide.
Soft or sandy ground. Go deeper and wider rather than relying on the concrete alone.

Metric: depth in centimetres

The same rule in metres: a third of the height, 60.96 cm minimum, 100 x 100 mm posts in a 300 mm hole, post lengths in the 0.3 m steps timber merchants stock (2.4, 2.7, 3.0 m).

100 x 100 mm posts, 300 mm hole
Fence height	Depth	Post needs	Buy	Concrete per hole	25 kg bags	20 kg bags
0.9 m	61 cm	1.51 m	1.8 m	41 L	4	5
1.2 m	61 cm	1.81 m	2.1 m	41 L	4	5
1.5 m	61 cm	2.11 m	2.4 m	41 L	4	5
1.8 m	61 cm	2.41 m	2.7 m	41 L	4	5
2.4 m	80 cm	3.2 m	3.3 m	53 L	5	6

Setting the post

Dig to depth plus 4 to 6 in, put gravel in the bottom and stand the post on it, so the end grain drains.
Brace the post plumb in two directions before the concrete goes in; fast-setting mix gives you about 20 minutes.
Fill to just above ground and slope the top away from the post, so water runs off instead of pooling at the wood.
Bag counts by hole size are in concrete per fence post.

Frequently asked questions

How deep should a post be for a 6 foot fence?: 24 inches, a third of the height, in a hole about 10 inches across for a 4x4. The post is 8 ft long, so buy 8 ft posts, and each hole takes 1.01 cubic feet of concrete: 2 bags of 80 lb or 3 of the 50 lb fast-setting mix.
How deep for an 8 foot fence?: 32 inches by the one-third rule, so the post needs 10.7 ft and you buy 12 ft posts. An 8 ft fence catches a lot of wind: use 6x6 posts at 6 ft centres, a 16 in hole, and 6 bags of 80 lb per post.
Is 2 feet deep enough for a fence post?: Yes for fences up to 6 ft in ground that does not freeze deeply, which is why 24 inches is the minimum here even for a 3 or 4 ft fence (a 4 ft picket fence still gets a 24 in hole and 6 ft posts). Go deeper for taller fences, gate and corner posts, sandy soil, and wherever the frost line is below 2 ft.
What is the frost line and why does it matter?: The depth to which the ground freezes in winter. Water in the soil expands as it freezes and lifts anything sitting above that depth, so a post footing that stops above the frost line is heaved a little every year until the fence leans. In the northern United States and Canada the frost line is 3 to 4 ft or more; the local building department publishes the figure and the code depth for posts.
How wide should the hole be?: About three times the width of the post: 10 in for a 4x4 (which is 3 1/2 in), 16 in for a 6x6. A wider hole means more concrete but a footing that resists leaning; a hole barely bigger than the post leaves too thin a collar of concrete to do anything.
Do fence posts need concrete?: Not always. Line posts in firm, well-drained soil can be set in compacted gravel, which drains and is easier to replace. Corner, end and gate posts, posts in soft or wet ground, and any fence over 5 ft should be concreted. In either case put 4 to 6 in of gravel in the bottom of the hole so the end grain is not standing in water, and crown the concrete so rain runs off the post.

How many fence posts do I need? (50 to 300 ft)
Posts, sections and rails for 50 to 300 ft of fence at 6 and 8 ft spacing, what a gate or a corner adds, the bags of concrete for the holes, and 10 to 100 m in metric.
How many pickets for a fence? (per section and per 100 ft)
Pickets per 6 and 8 ft section and per 100 ft for 3 1/2 and 5 1/2 in boards at 0 to 3 1/2 in gaps, with waste, screws per picket, and the metric board counts.
How much does a cinder block garage cost? (blocks, mortar, grout and slab for 1, 2 and 3 car)
Blocks, mortar and grout for 1 to 3 car block garages, 12x20 to 36x24 ft, 8 ft walls, doors and windows taken off, plus the 4 in slab, at 2026 prices.
How much does a ton of gravel cover? (at 2, 3 and 4 inches, by stone)
A ton of 3/4 in crushed stone is 0.79 cubic yards: about 85 sq ft at 3 in, 128 at 2 in, 64 at 4 in. Coverage by stone, tons for 100 to 1,000 sq ft, price.

Last updated 2026-09-14. Figures are planning estimates from typical product data: check the yield, size or coverage printed on what you buy and round up.