Framing & structure
Joist notch & hole calculator
Check a notch or bored hole in a sawn joist against the IRC depth, length, edge-distance and middle-third limits.
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What the joist notch and hole calculator checks
A joist notch and hole calculator tells you how big a notch or a bored hole can be in a sawn lumber joist, and where along the span it is allowed. Enter the joist size, the clear span and the cut you plan to make, and it returns the maximum notch depth and length, the end-notch limit, the largest hole, the no-notch zone in the middle third of the span, and a pass or fail for each rule.
The limits come from 2021 IRC R502.8.1. Notches may be up to one-sixth of the depth, no longer than one-third of the depth, and never in the middle third of the span. Notches at the ends of a joist may be up to one-quarter of the depth. Bored holes may be up to one-third of the depth and must stay at least 2 in from the top and bottom edges and from any other hole or notch. On a 2x10, which is 9¼ in deep, that means notches up to 1.54 in deep and holes up to 3.08 in in diameter.
The rules are fractions of the actual depth, not the nominal size, and they apply to sawn lumber only. I-joists, LVL, glulam and trusses may only be cut where the manufacturer or a design professional allows, and studs follow different rules. The calculator is a quick check against the code text, not an engineering analysis; your building official and engineer of record have the final say.
How to use the joist notch & hole calculator
- Choose Imperial or Metric. Imperial is the default, and your choice carries across the free tools.
- Pick the Joist size (2x6 to 2x12, or 45 mm metric joists), or choose Custom and enter the Joist thickness and Joist depth as actual dressed dimensions. Enter the Clear span between supports.
- Choose the Cut: a bored hole, a notch on the top or bottom edge, or an end notch over a support. For holes and span notches, enter the Distance from the nearer support to the hole centre or to the near edge of the notch.
- Enter the Hole diameter and the Top edge to hole distance, or the Notch depth and Notch length. If another hole or notch is close by, set Other holes or notches nearby to Yes and enter the Clear distance to the nearest one.
- Read the maximum notch, end-notch and hole sizes, the start and end of the no-notch zone and the result for each rule, then check the elevation diagram. Download the PDF, CSV or SVG, or copy the result into a site note or RFI.
Worked example
Imperial: A 2x10 (9¼ in deep) on a 14 ft span allows notches up to 1.54 in deep and 3.08 in long outside the middle third (4.67–9.33 ft from a support), end notches up to 2.31 in and holes up to 3.08 in in diameter, at least 2 in from either edge.
Metric: A 45 × 240 mm joist on a 4.2 m span allows notches up to 40 mm deep and 80 mm long outside the middle third (1.4–2.8 m from a support), end notches up to 60 mm and holes up to 80 mm in diameter.
IRC rules for notching and boring floor joists
Section R502.8.1 of the 2021 International Residential Code covers sawn lumber joists, rafters and beams. It limits notches and holes by fractions of the member's depth, keeps notches out of the middle third of the span where bending stress is highest, and keeps holes away from the edges where the top and bottom fibres do most of the work.
The same limits have been in the IRC for several editions. Local amendments can change them, and some jurisdictions add their own drawings or require an engineer for any cut in a floor that carries a bearing wall, so confirm the adopted text before cutting.
| Cut | Limit | Where it applies |
|---|---|---|
| Notch depth | ≤ 1/6 of the joist depth | Anywhere outside the middle third |
| Notch length | ≤ 1/3 of the joist depth | Notches along the span |
| Notch location | Not in the middle third of the span | Top or bottom edge |
| End notch depth | ≤ 1/4 of the joist depth | At the ends of the member |
| Tension edge of thick members | No notches except at the ends | Members 4 in nominal or thicker |
| Hole diameter | ≤ 1/3 of the joist depth | Bored or cut holes |
| Hole edge distance | ≥ 2 in to the top, the bottom, another hole or a notch | Bored or cut holes |
Maximum notch and hole sizes by joist size
These are the limits the calculator returns for common joists, using actual dressed depths. The largest centred hole is the smaller of one-third of the depth and the depth less 2 in at each edge; only the 2x6 and the 140 mm joist are limited by the edge distance.
Round down when you mark out a cut. A 2x8's one-sixth limit is 1.21 in, so a 1¼ in notch is already over.
| Joist | Depth | Max notch depth (1/6) | Max notch length (1/3) | Max end notch (1/4) | Largest centred hole |
|---|---|---|---|---|---|
| 2x6 | 5½ in | 0.92 in | 1.83 in | 1.38 in | 1.50 in |
| 2x8 | 7¼ in | 1.21 in | 2.42 in | 1.81 in | 2.42 in |
| 2x10 | 9¼ in | 1.54 in | 3.08 in | 2.31 in | 3.08 in |
| 2x12 | 11¼ in | 1.88 in | 3.75 in | 2.81 in | 3.75 in |
| 45 × 140 mm | 140 mm | 23 mm | 47 mm | 35 mm | 38 mm |
| 45 × 190 mm | 190 mm | 32 mm | 63 mm | 48 mm | 63 mm |
| 45 × 240 mm | 240 mm | 40 mm | 80 mm | 60 mm | 80 mm |
| 45 × 290 mm | 290 mm | 48 mm | 97 mm | 73 mm | 97 mm |
Why the middle third and the end notch matter
A uniformly loaded joist has its largest bending moment at mid-span. The top edge is in compression and the bottom edge in tension, and both edges carry the most stress there, which is why the code keeps notches out of the middle third. Holes near mid-depth remove wood close to the neutral axis, where bending stress is low, so the IRC does not restrict where along the span they go.
Near the supports the problem is shear. A notch on the bottom edge at a bearing leaves less wood to carry the end reaction and starts a crack at the re-entrant corner. NDS 2018 section 3.4.3.2 reduces the allowable end shear at a tension-side notch to (dn/d)² of the unnotched value, where dn is the depth left. The calculator reports that percentage for end notches.
| End notch depth | Depth left | Shear capacity left |
|---|---|---|
| 1 in | 8¼ in | 79.5% |
| 1½ in | 7¾ in | 70.2% |
| 2 in | 7¼ in | 61.4% |
| 2-5/16 in (the 1/4 limit) | 6-15/16 in | 56.3% |
Studs, rafters and engineered joists follow different rules
R502.8.1 applies to sawn joists, rafters and beams. Wall studs are covered by R602.6, which measures cuts against the stud's width rather than its depth. Engineered wood products are covered by R502.8.2: cuts, notches and holes are not permitted unless the manufacturer's recommendations or a registered design professional allow them. Trusses may not be cut, notched, drilled or otherwise altered without a registered design professional's approval (R502.11.3).
I-joist manufacturers publish hole charts that allow surprisingly large holes in the web, but never in the flanges, and with minimum distances from supports that depend on the span and the hole size. Use the chart for the exact series and depth on site.
| Member | Notches | Holes | Source |
|---|---|---|---|
| Stud in an exterior wall or bearing partition | ≤ 25% of the width (⅞ in in a 2x4) | ≤ 40% of the width, or up to 60% if the stud is doubled | R602.6 |
| Stud in a non-bearing partition | ≤ 40% of the width (1.4 in in a 2x4) | ≤ 60% of the width (2.1 in in a 2x4) | R602.6 |
| Any bored stud | Not in the same section as a hole | Edge of the hole at least ⅝ in from the edge of the stud | R602.6 |
| I-joists, LVL, glulam | Not permitted unless allowed | Manufacturer's hole chart or design professional | R502.8.2 |
| Trusses | Not permitted | Only with a registered design professional's approval | R502.11.3 |
Worked example: a drain and a pipe notch in a 2x10
A plumber needs to cross a 2x10 floor on a 14 ft span with a 3 in drain and to notch the top of one joist for a ¾ in supply line. The calculator's limits are 1.54 in deep and 3.08 in long for the notch, with no notching between 4 ft 8 in and 9 ft 4 in from either support, and a 3.08 in maximum hole.
A 3 in hole centred in the depth leaves 3⅛ in above and below, so it is within both the one-third limit and the 2 in edge distances. A 3½ in hole is over one-third of the depth and fails, so a larger drain has to run below or parallel to the joists. A 1¼ in deep, 3 in long top notch 2 ft from the bearing ends at 2 ft 3 in, inside the outer third, and passes. Moving it to 5 ft from the support puts it in the middle third, and the calculator marks it outside the rules.
Who it is for and when to use it
Plumbing and electrical rough-in
Size drain, vent and conduit holes before drilling, and find where notches for supply lines are allowed, so the framing inspection does not fail on cut joists.
Renovations and alterations
Check an existing cut found when opening a ceiling, record the result in a site note, and decide whether the joist needs reinforcement or an engineer's review.
Inspection and RFI responses
Turn an on-site question into a clear table of limits, entered sizes and results to attach to an RFI or inspection note.
Planning service routes in design
Decide early whether a duct or drain can pass through the joists or needs a dropped ceiling or a joist run in the other direction. Pair it with the floor joist span calculator when choosing the joist depth.
Method, formulas & assumptions
Limits are fractions of the actual joist depth d (2021 IRC R502.8.1): notch depth ≤ d/6, notch length ≤ d/3, no notches in the middle third of the clear span (L/3 to 2L/3), end notches ≤ d/4, no tension-edge notches in members 4 in nominal or thicker except at the ends; hole diameter ≤ d/3 with at least 2 in to the top and bottom edges and to any other hole or notch. Largest centred hole = min(d/3, d − 2 × 2 in). End notches also report the NDS 3.4.3.2 shear reduction (dn/d)².
Imperial inputs are converted with exact factors (1 ft = 0.3048 m, 1 lb = 0.45359237 kg, 1 US gal = 3.785411784 L) before the calculation runs in SI, then results are converted back.
Common mistakes to avoid
- Using the nominal depth. A 2x10 is 9¼ in deep, so the hole limit is 3.08 in, not 3⅓ in.
- Notching in the middle third. The middle third is measured on the clear span between supports, not on the length of the board.
- Drilling too close to the edge. A hole that meets the one-third diameter limit can still fail the 2 in edge distance on a 2x6 or a shallow metric joist.
- Stacking cuts close together. Holes must be at least 2 in apart and 2 in from any notch, edge to edge.
- Applying sawn-lumber rules to I-joists, LVL or trusses. Those products follow the manufacturer's chart or need a design professional.
- Assuming the rules cover every load case. Joists carrying a bearing wall, a point load or a cantilever may need an engineer even when the cut meets the code fractions.
Scope & limits
Sawn lumber joists, rafters and beams only. I-joists, LVL, glulam and trusses follow the manufacturer's hole chart or a design professional (R502.8.2, R502.11.3); studs follow R602.6. Joists carrying bearing walls, point loads or cantilevers, reinforcement and repairs are not assessed. Local amendments, the building official and the engineer of record govern.
Frequently asked questions
How big a hole can I drill in a 2x10 joist?
Up to one-third of the depth under IRC R502.8.1. A 2x10 is 9¼ in deep, so the maximum is 3.08 in, and the hole must stay at least 2 in from the top and bottom edges.
How deep can you notch a floor joist?
Up to one-sixth of the joist depth along the span, outside the middle third, and no longer than one-third of the depth. At the ends of a joist the limit is one-quarter of the depth.
Where can you not notch a joist?
Not in the middle third of the span, and not on the bottom (tension) edge of members 4 in nominal or thicker except at the ends. The calculator shows the middle-third zone for your span.
Can I drill a hole anywhere along a joist?
The IRC does not limit where along the span a hole goes, only its size and its distance from the edges, other holes and notches. Keeping holes near mid-depth and away from bearings and point loads is good practice.
Do these rules apply to I-joists?
No. IRC R502.8.2 prohibits cuts, notches and holes in engineered wood products unless the manufacturer or a design professional allows them. Use the hole chart for the exact I-joist series and depth.
How much can you notch a stud?
Studs follow IRC R602.6: up to 25% of the width in exterior and bearing walls and 40% in non-bearing partitions. Bored holes may be up to 60% of the width, with bearing-wall studs over 40% doubled.
Does the calculator work in metric?
Yes. Switch to Metric for millimetres and metres. A 45 × 240 mm joist allows 40 mm notches, 60 mm end notches and 80 mm holes, with 2 in (50.8 mm) edge distances.
What if a joist has already been cut too much?
Do not rely on it. Common fixes include sistering a new joist, adding blocking or a header, or an engineered repair, and an engineer or the building official should approve the repair.
Do I need an account to download the result?
No. All calculations, local file processing and exports on this page are free, without an account.
Where are my inputs stored?
The tool keeps inputs in this browser tab. It does not upload them or create a cloud copy. Save or download anything you want to keep before leaving the page. Standard site analytics may operate independently of the tool.
Can I work in metric instead of imperial?
Yes. Use the Imperial / Metric switch above the inputs. Imperial (feet, inches, pounds, gallons) is the default; switching converts every dimensional field and result, and your choice is remembered across the free tools in this browser.
Further reading
- Renovations and extensions
- Building permit process explained
- All framing & structure tools
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