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Post-Installed Concrete Anchor Drill Depth Calculator

Turn a required effective embedment into the depth to drill, and check the anchor you have reaches it once the fixture and the nut are allowed for.

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  • Every formula cited
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Whether the anchor comes at a fixed length or is cut from stock rod on site.

The distinction decides whether the anchor length constrains you. A wedge or screw anchor arrives at a length the catalogue fixed, so it either reaches the embedment or it does not. A threaded rod is cut, so the question turns around: the calculator reports the length to cut rather than a shortfall.

The embedment the design calls for, measured from the concrete surface.

This is the value the capacity was taken at — change it and every published tension and shear figure for the anchor changes with it. Take it from the design, then confirm the evaluation report actually lists that embedment for the diameter you are installing; interpolating between tabulated embedments is not permitted.

The extra depth the evaluation report asks for beyond the embedment itself.

Mechanical anchors need a hole deeper than the embedment so cuttings can fall clear of the tip and the anchor can be driven fully home; the report tabulates this as a minimum hole depth against each embedment. For adhesive anchors the hole is normally drilled to the embedment and no deeper, because the adhesive volume is set by it — enter zero in that case.

The overall length of the anchor or rod you have, tip to head.

The catalogue length is the whole piece of steel, and none of it is embedment until the fixture and the nut have taken their share. This is exactly where anchors get set short: the length reads generously against the embedment and then loses a third of itself to a base plate nobody subtracted.

The combined thickness of everything the anchor passes through before the concrete.

Add up the whole stack: base plate, shim pack, levelling grout, sole plate, any packing. Grout under a base plate is the item most often left out, and it is often thicker than the plate above it.

What has to stand above the fixture: washer, nut, and thread run-out past it.

A washer and a hex nut together take up most of the anchor diameter again, and torque-controlled anchors need thread showing above the nut after setting so the wedges can draw up. Leaving nothing to project is how an anchor ends up unable to reach torque.

Required drilled hole depth

3.34 in

High confidence

The anchor entered leaves 3.36 in of embedment, which covers the 2.75 in required. Drill and clean the hole to the depth above, not to the anchor. Hole depth, diameter and cleaning regime are all part of the qualification — an uncleaned hole in an adhesive anchor loses a large fraction of its bond, and no arithmetic here recovers it.

Embedment available from the anchor entered
3.36 in
Anchor length needed for this embedment
3.89 in
Shortfall against the required embedment
0 in
Drilled depth beyond the embedment
0.59 in
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • ACI 355.2 (qualification of post-installed mechanical anchors) and ACI 355.4 (qualification of adhesive anchors): an anchor's published capacity belongs to one qualified embedment and one installation procedure, both stated in the product's ICC-ES evaluation report
  • ACI 318 Chapter 17 requires post-installed anchors to be installed in accordance with the manufacturer's printed installation instructions (MPII), which give the minimum hole depth for each anchor diameter and embedment
  • Arithmetic only: hole depth = effective embedment + the additional depth the evaluation report specifies; embedment available = anchor length − fixture thickness − the nut, washer and thread projection above it

Inputs used

Anchor Supply Form
Supplied at a fixed length (wedge, sleeve or screw anchor)
Required Effective Embedment
2.75 in
Additional Hole Depth Beyond the Embedment
0.59 in
Nominal Anchor or Rod Length
4.5 in
Fixture and Plate Thickness
0.39 in
Nut, Washer and Thread Projection
0.75 in

Intermediate steps

Embedment available from the anchor entered
3.36 in
Anchor length needed for this embedment
3.89 in
Shortfall against the required embedment
0 in
Drilled depth beyond the embedment
0.59 in
Final result3.34 in

Confidence note: The anchor entered leaves 3.36 in of embedment, which covers the 2.75 in required. Drill and clean the hole to the depth above, not to the anchor. Hole depth, diameter and cleaning regime are all part of the qualification — an uncleaned hole in an adhesive anchor loses a large fraction of its bond, and no arithmetic here recovers it.

What this calculation does not cover

  • Does not check capacity. Whether the embedment is adequate for the load is an ACI 318 Chapter 17 calculation involving concrete breakout, pryout, edge distance, spacing and whether the concrete is cracked.
  • Does not check that the base material is thick enough. Most reports set a minimum member thickness well above the hole depth, and drilling through a slab is a different problem entirely.

Add the equipment this sizes

This result is a specification — 3.34 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

4.5 in
Schematic, drawn to the proportions you entered — not to scale on screen.

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 2026-08-30 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations3
  1. ACI 355.2 (qualification of post-installed mechanical anchors) and ACI 355.4 (qualification of adhesive anchors): an anchor's published capacity belongs to one qualified embedment and one installation procedure, both stated in the product's ICC-ES evaluation report
  2. ACI 318 Chapter 17 requires post-installed anchors to be installed in accordance with the manufacturer's printed installation instructions (MPII), which give the minimum hole depth for each anchor diameter and embedment
  3. Arithmetic only: hole depth = effective embedment + the additional depth the evaluation report specifies; embedment available = anchor length − fixture thickness − the nut, washer and thread projection above it

Which documents these citations point at

Standards referenced: ACI 355.2, ACI 355.4, ACI 318 (American Concrete Institute, United States).

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.

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? Anchor and fixing — the term in each market, how close the equivalence really is, and the standard that governs it.

Still deciding? Cast-In Anchor Bolts vs Post-Installed Anchors — the factors that actually differ, with no invented prices.

How to calculate post-installed concrete anchor drill depth in 7 steps

  1. Anchor Supply FormWhether the anchor comes at a fixed length or is cut from stock rod on site.
  2. Required Effective EmbedmentThe embedment the design calls for, measured from the concrete surface.
  3. Additional Hole Depth Beyond the EmbedmentThe extra depth the evaluation report asks for beyond the embedment itself.
  4. Nominal Anchor or Rod LengthThe overall length of the anchor or rod you have, tip to head.
  5. Fixture and Plate ThicknessThe combined thickness of everything the anchor passes through before the concrete.
  6. Nut, Washer and Thread ProjectionWhat has to stand above the fixture: washer, nut, and thread run-out past it.
  7. Required drilled hole depthThe tool computes the required drilled hole depth from those figures and shows the formula, its sources, and a confidence rating alongside it.

Required drilled hole depth by required effective embedment

Page defaults, not your figures above.

Required Effective EmbedmentRequired drilled hole depth (in)
2 in2.59
3 in3.59
4 in4.59
5 in5.59

Frequently asked questions

Why is the drilled hole deeper than the embedment for a mechanical anchor?
Because the dust the bit produces has to go somewhere. Cuttings pack into the bottom of the hole and stop the anchor being driven fully home, which quietly reduces the embedment below what the design assumed. The evaluation report handles this by tabulating a minimum hole depth greater than the embedment, and that difference is what the extra-depth field carries.
My anchor is 15 mm short of the embedment. Can I just torque it harder?
No — torque sets the anchor, it does not create embedment. Concrete breakout capacity scales roughly with embedment to the power of 1.5, so losing 15 mm from a 70 mm embedment costs about a third of the tension capacity, and torquing a shallow anchor harder is more likely to pull the cone than to fix anything. Use the next length up.
Does the embedment for an adhesive anchor include the fixture thickness?
It does not. Effective embedment is measured from the concrete surface downward, so anything between the nut and the concrete — plate, grout, shims, sole plate — is outside it and has to be added to the rod length separately. That subtraction is the single commonest reason a rod that looked long enough on paper ends up set shallow.
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.