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Post Hole Concrete Calculator

Work out the concrete for a set of post holes, allowing for the volume the post itself displaces.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
Diameter of the augered hole.

Roughly three times the post width is the usual rule — a 100 mm post in a 300 mm hole. Wider gives more resistance to overturning, which is what actually holds a fence up in wind.

Depth of the hole.

One third of the above-ground post height is the usual starting point. Where ground freezes, the footing must go below the frost line regardless — a shallower one will be lifted by frost heave, and no amount of concrete prevents it.

Width of the post, to deduct its volume.

A square post is assumed. The deduction is small per hole and adds up across a fence run.

How many holes.

Holes, which is not the number of bays and not always the number of posts. A fence of N bays needs N+1 posts, so counting panels leaves one hole unordered at the end of every run. End, corner and gate posts normally take a larger and deeper hole than intermediate ones, so where the run has several of them it is worth pricing those separately rather than averaging them into this count.

Bag you are buying.

Yields are approximate and vary with the mix; check the bag.

Concrete required

0.475 yd³

Medium confidence

Geometry with the post volume deducted. Bag yields are nominal and vary with the mix and how wet it is made.

Per hole
0.05 yd³
Bags required
39 bags
Post displacement deducted
0.08 yd³
Cubic yards
0.48 yd³
Approximate weight
1,923.49 lb
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • Common practice: hole diameter three times the post width; embedment one third of the above-ground height, or below frost depth where that is deeper
  • IRC R403.1.4 requires footings below the local frost line — the governing figure where ground freezes

Inputs used

Hole diameter
11.75 in
Hole depth
2 ft
Post width
4 in
Number of posts
10
Bag size
20 kg bag (~0.0094 m³ mixed)

Intermediate steps

Per hole
0.05 yd³
Bags required
39 bags
Post displacement deducted
0.08 yd³
Cubic yards
0.48 yd³
Approximate weight
1,923.49 lb
Final result0.48 yd³

Confidence note: Geometry with the post volume deducted. Bag yields are nominal and vary with the mix and how wet it is made.

What this calculation does not cover

  • Frost depth governs where ground freezes and overrides any rule-of-thumb embedment. Check the local requirement.
  • Soft or made ground needs a wider or deeper footing than these proportions suggest; overturning resistance comes from the soil, not the concrete.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

plan: 10 post holes11.75 in298.45 mm2 ft0.61 m

Part of bigger jobs

This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.

Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations2
  1. Common practice: hole diameter three times the post width; embedment one third of the above-ground height, or below frost depth where that is deeper
  2. IRC R403.1.4 requires footings below the local frost line — the governing figure where ground freezes

Which documents these citations point at

  • International Residential Code — R403.1.4 (United States)One- and two-family dwellings and townhouses up to three storeys — structure, fire safety, energy, plumbing, mechanical and electrical in a single document.

A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To place and finish concrete, erect formwork, saw-cut cured concrete, excavate by hand and set fence posts. Generic types, no brands, no prices.

Protection this work requires

  • Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
  • Hardwood dust is a recognised carcinogen: extract at the tool and wear a P2/N95 respirator when cutting or sanding indoors.
  • Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
  • Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
  • Breakers and grinders cause permanent nerve damage: limit continuous trigger time, keep hands warm, and stop if fingers tingle or blanch.
  • Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.
  • Digging blind strikes gas, water and power every day: get the plans, scan with a cable avoidance tool, and hand-dig trial holes over anything you find.
Show the 21 tools this job needs

Essential

  • Angle grinder

  • Bull float and edger

  • Cable and pipe detector

  • Circular saw

  • Claw hammer

  • Dust extractor or vacuum with a fine filter

  • Mixing bucket or tub

  • Post hole digger or auger

  • Screed bar or rail

  • Shovel and spade

  • Spirit level

  • String line and pins

  • Tape measure

  • Wheelbarrow

Recommended

  • Chalk line

  • Cordless drill/driver

  • Floor or cut-off saw

  • Plate compactor

  • Post driver

  • SDS rotary hammer

Optional

  • Power float

Also needed as materials: chalk refill, circular saw blades, cutting and diamond discs, diamond blades, drill and driver bits, SDS bits and chisels.

what each concrete tool is for and what each groundwork tool is for and what each landscaping tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Called something else where you work? Footing and foundation — the term in each market, how close the equivalence really is, and the standard that governs it.

Still deciding? Concrete vs Gravel for Setting Fence Posts — the factors that actually differ, with no invented prices.

Worked example: Privacy fence — step 4 of 7

Already gone wrong? My fence posts are rotting or the fence is leaning

The data behind it: Production rates by operation

How to calculate post hole concrete in 6 steps

  1. Hole diameterDiameter of the augered hole.
  2. Hole depthDepth of the hole.
  3. Post widthWidth of the post, to deduct its volume.
  4. Number of postsHow many holes.
  5. Bag sizeBag you are buying.
  6. Concrete requiredThe tool computes the concrete required from those figures and shows the formula, its sources, and a confidence rating alongside it.

Concrete required by hole diameter

Page defaults, not your figures above.

Hole diameterConcrete required (yd³)
5 in0.021
10 in0.319
15 in0.816
20 in1.51

Frequently asked questions

How deep should a fence post go?
A third of the above-ground height is the usual rule — a 1.8 m fence wants about 600 mm of embedment. Where the ground freezes, that rule is overridden by frost depth: the footing must sit below the frost line or heave will lift it, and no amount of concrete stops that.
Should concrete go all the way to the top of the hole?
Finish slightly proud and slope it away from the post so water runs off. A concrete collar that dishes toward the post holds water against the timber and rots it exactly where it matters. Some prefer a gravel base under the post so water drains rather than sitting in a concrete cup.
Is a wider hole better than a deeper one?
For wind, often yes. A fence post fails by rotating, and resistance to overturning grows with the diameter of the mass in the ground. For frost, depth is what matters and width does nothing. Which one governs depends on your climate.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.