Post Setting Sheet
Work out the holes, mark the run, and take one bag count to the yard. The depth column is the one worth checking twice.
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The job
- Location
- Date
- Post size
- Hole diameter
- Hole depth
- Number of posts
- Bag yield
- BAGS
- Frost line depth (local)
One row per post — depths often vary along a run
| Post | Depth dug | Anything hit? | Hole wider than planned? | Set / plumb ✓ |
|---|---|---|---|---|
The arithmetic
- Hole volume
- pi/4 x diameter² x depth (cubic inches)
- Post volume
- width² x depth, for a square post
- Concrete
- hole - post
- To cubic feet
- divide by 1728
- To cubic yards
- divide by 27 again
- Bags
- cubic feet / yield per bag, rounded UP
- ⚠ Diameter
- volume rises with its SQUARE
- 10in → 12in hole
- 44% more VOLUME (55% more concrete with a 4in post)
Rules of thumb (starting points, not requirements)
- Depth below ground
- about 1/3 of the post's total length
- Hole width
- about 3x the post width
- Frost line
- LOCAL requirement — check it, do not guess
- Bags vs ready-mix
- under about 0.5 cu yd, use bags
Before you start digging
- UTILITIES LOCATED — call before you dig, every time
- Frost line depth checked for your area
- Property line confirmed if the fence is near it
- Post spacing set out and string line run
- Post height planned so 1/3 of the total is below ground
- Auger bit size decided — it is a bigger cost lever than it looks
- Gravel for drainage at the base if your soil holds water
- One or two spare bags bought — holes only ever get bigger
- Posts braced plumb before the concrete goes off
Locate the utilities first
Everything else on this sheet is arithmetic. This one is not. Buried services do not announce themselves, an auger finds them very efficiently, and the consequences range from an expensive afternoon to a fatal one. Free location services exist in most places and take a phone call.
Holes get bigger, never smaller
A hole that hits a root or a rock ends up wider than planned, and a dug hole is not something you can leave open while you drive back for more concrete. That asymmetry is the whole argument for a spare bag or two — the downside of having one left over is trivial next to the downside of being one short.