Rule of thumb: the hole is about three times the post width and at least one third of the post height deep, and below the frost line in cold climates.
How the fence calculator works
FenceCalc splits each run into sections no longer than the post spacing, rounding up. Posts are the sections plus one, minus one for each corner shared by two runs, plus one extra post per gate. Rails are sections × rails per section. Pickets are the fence length minus the gate openings, in inches, divided by picket width plus gap, rounded up.
Concrete per hole is the hole's volume minus the post's, from the top of a 6-inch gravel base (if you include one) to ground level, divided by the bag yield and rounded up to whole bags.
Typical wood fence specs
| Fence | Posts | Rails | Pickets |
|---|---|---|---|
| 4 ft picket fence | 4×4, 6 ft long, 6–8 ft apart | 2 per section | 1×4, 2–3″ gaps |
| 6 ft privacy fence | 4×4, 8 ft long, 8 ft apart | 3 per section | 1×6, no gap |
| Gate posts | 4×4 or 6×6, set deeper | — | — |
Concrete bag yields
| Bag | Yield |
|---|---|
| 40 lb | 0.30 ft³ |
| 50 lb | 0.375 ft³ |
| 60 lb | 0.45 ft³ |
| 80 lb | 0.60 ft³ |
Yields are the published figures for Quikrete fast-setting and standard concrete mixes. Results are estimates: buy a few spare pickets and a spare bag, and check local codes, frost depth, HOA rules and underground utilities (call 811 in the US) before you dig.
Frequently asked questions
How many bags of concrete per fence post?
About two 50 lb bags or one and a half 60 lb bags for a 4×4 in a 10-inch hole 2 ft deep.
Should I put gravel under fence posts?
Yes, around 6 inches of gravel lets water drain away from the end of the post.
Do I need to mix fast-setting concrete?
No. Pour the dry mix into the hole and add water as the bag directs.
Is FenceCalc free?
Yes, with no sign-up or ads.
Are my measurements saved?
Yes, in this browser only.