ACI 318-25 & CRSI IPG5.1-2026 Reference

Rebar Hook Length Chart 2026: 90°, 135° & 180° | ACI 318 Chart

Standard 90-degree, 180-degree, and 135-degree hook geometry for reinforcing bars: minimum bend diameter, straight extension, and detailing dimensions under ACI 318-25 Table 25.3.1 and 25.3.2.

Bar Sizes #3 to #18 90° / 135° / 180° Hooks Seismic Hook Geometry Inches & Millimeters

Reviewed by Muhammad Ramzan Babar, PhD Researcher (Plasma Physics) & Calculator Developer – View Profile

Rebar Hook Length Chart: Quick Reference

Standard reinforcing bar hooks fall into two distinct families: longitudinal end hooks (90° and 180°) used to anchor the end of a main bar, and stirrup/tie/hoop hooks (90°, 135°, and 180°) used for transverse reinforcement. These use different ACI 318-25 tables and should never be read from the same row.

Standard 90° and 180° Longitudinal End Hook Chart

Stirrup and Tie Hook Quick Chart

What Is a Rebar Hook?

A rebar hook is a 90-degree or 180-degree bend at the free end of a reinforcing bar, formed specifically to provide anchorage in concrete. For stirrups and column ties, 90-degree and 135-degree bends are used instead, since transverse reinforcement serves a confinement function rather than a straight-embedment anchorage function.

Why Hooks Are Used

• Anchorage where straight embedment length is physically constrained, such as at a shallow footing edge or a narrow beam-column joint.
• Termination of a bar at a support or discontinuous edge.
• Force transfer through combined bond and bearing action at the bend.
• Closure of transverse reinforcement (stirrups, ties, hoops) around longitudinal bars.
• Confinement of the concrete core in columns and beam-column joints.

A hook does not automatically replace whatever straight development length a design otherwise requires. The applicable ACI 318-25 anchorage provision must still be satisfied.

What Does “Rebar Hook Length” Actually Mean?

Generic searches for “rebar hook length” can mean any of four different dimensions. Confusing them is the single most common error on this topic.

This chart focuses on the first two, geometry, and touches the third for context. For the fourth, see the dedicated section below and the full Rebar Development Length Chart.

Hook Extension vs Hook Development Length

This is the single most important distinction on this page.

90-Degree Rebar Hook Chart

Full lookup for standard 90-degree longitudinal end hooks across all current ACI 318-25 bar-size groups. CRSI fabrication references may show slightly different rounded A/G dimensions for shop drawings; ACI minimums shown here are the code-required geometry.

180-Degree Rebar Hook Chart

The 180-degree standard hook uses the rule l_ext ≥ max(4d_b, 2.5 in) for ordinary longitudinal bars.

Why 180° Hook Dimensions Differ from 90°

The 180-degree hook returns the bar back on itself, so its required straight tail is shorter than the 90-degree hook’s tail at the same bar size. This reflects the different bend geometry, not necessarily a difference in required structural embedment. Both hook types still require their own separate development length check under ACI 318-25 Section 25.4.3.

90° vs 180° Rebar Hooks

Neither hook type is universally stronger. The correct choice depends on available space, bar congestion, and the structural detailing shown on the project drawings.

Rebar Hook Bend Diameter Chart

Minimum inside bend diameter for standard longitudinal hooks is grouped by bar size under ACI 318-25 Table 25.3.1.

Inside bend diameter, bend radius, and the outside dimension of a bent bar are three different measurements. They should never be substituted for one another when reading a shop drawing.

Inside Bend Diameter vs Bend Radius

If the minimum inside bend diameter is D = 6d_b, the corresponding inside bend radius is R = D / 2 = 3d_b. Fabrication drawings typically reference whichever convention (diameter or radius) matches the applicable detailing standard, so always confirm which one a given drawing is using before bending a bar or checking a fabricated shape. Measuring the outside of a bent bar with a tape will give a different, larger number than either the inside bend diameter or the inside bend radius, because it includes the bar’s own material thickness on both sides of the curve.

Rebar Hook Length by Bar Size

#3 and #4 Hooks

#3 (d_b = 0.375 in): bend diameter 2.25 in, 90° extension 4.50 in, 180° extension 2.50 in. #4 (d_b = 0.500 in): bend diameter 3.00 in, 90° extension 6.00 in, 180° extension 2.50 in.

#5 and #6 Hooks

#5 (d_b = 0.625 in): bend diameter 3.75 in, 90° extension 7.50 in, 180° extension 2.50 in. #6 (d_b = 0.750 in): bend diameter 4.50 in, 90° extension 9.00 in, 180° extension 3.00 in.

#7 and #8 Hooks

#7 (d_b = 0.875 in): bend diameter 5.25 in, 90° extension 10.50 in, 180° extension 3.50 in. #8 (d_b = 1.000 in): bend diameter 6.00 in, 90° extension 12.00 in, 180° extension 4.00 in. #8 is the largest bar still in the 6d_b bend-diameter group.

#9 through #11 Hooks

At #9 and larger, the bend diameter group changes to 8d_b. #9 (d_b = 1.128 in): bend diameter 9.02 in. #10 (d_b = 1.270 in): bend diameter 10.16 in. #11 (d_b = 1.410 in): bend diameter 11.28 in. The 12d_b and 4d_b/2.5 in extension rules still apply the same way across all groups.

#14 and #18 Hooks

These largest ordinary bar sizes use a 10d_b bend diameter. #14 (d_b = 1.693 in): bend diameter 16.93 in. #18 (d_b = 2.257 in): bend diameter 22.57 in, the largest standard hook geometry ACI 318-25 Table 25.3.1 explicitly covers.

Hook Dimensions in Inches and Millimeters

Metric values here are direct unit conversions of the U.S. customary ACI 318-25 requirements, calculated for reference. ACI 318 and ACI 318M each have their own native rounded metric bar sizes and hook tables; do not mix a rounded ACI 318M metric bar designation with these converted inch-based values without checking the ACI 318M table directly.

What About #20 Rebar Hooks?

If a project genuinely specifies #20 reinforcement with a hooked end, that detail requires specific engineering approval rather than a generic chart lookup.

Stirrup and Tie Hook Length Chart

Transverse reinforcement, stirrups, ties, and hoops, uses its own hook geometry table, ACI 318-25 Table 25.3.2, separate from the longitudinal end-hook table above.

90°, 135°, and 180° Stirrup and Tie Hooks

90° Stirrup and Tie Hooks

For #3 through #5 transverse bars, minimum inside bend diameter is 4d_b and the extension is the greater of 6d_b or 3 in. For the larger #6 through #8 transverse bars, ACI 318-25 uses a 6d_b bend diameter and a 12d_b extension, a different rule than the smaller sizes. Do not merge these values with the longitudinal 90-degree end-hook dimensions shown earlier on this page.

135° Stirrup and Tie Hooks

The 135-degree hook is the primary confinement detail for stirrups, ties, and hoops. It is required, not optional, for seismic hooks on any hoop shape except circular hoops. For #3 through #5, bend diameter is 4d_b with an extension of the greater of 6d_b or 3 in. For #6 through #8, bend diameter is 6d_b with the same extension rule. A 135-degree stirrup hook is not the ordinary longitudinal-bar standard end hook covered earlier on this page; it belongs to a separate table and a separate structural function.

180° Stirrup and Tie Hooks

ACI 318-25 also provides 180-degree geometry for closed ties and hoops, using the same bend-diameter groups as the 90-degree and 135-degree stirrup hooks (4d_b for #3 through #5, 6d_b for #6 through #8) but the extension rule matches the longitudinal 180-degree rule: greater of 4d_b or 2.5 in. Do not assume the longitudinal #3 through #18 end-hook chart applies to these bars.

Standard Hooks vs Seismic Hooks

ACI 318-25 defines a seismic hook as a hook on a stirrup, hoop, or crosstie with a bend of at least 135 degrees, except circular hoops, which may use a bend of at least 90 degrees. A seismic hook must have an extension of at least 6d_b, not less than 3 in, that engages the longitudinal reinforcement and projects into the interior of the stirrup or hoop.

Ordinary Transverse Hook

An ordinary 90-degree, 135-degree, or 180-degree stirrup or tie hook satisfies the geometry in Table 25.3.2 for that bar size and angle, without necessarily engaging the longitudinal bar or projecting into the confined core in the specific way a seismic hook requires.

Seismic Hook

A seismic hook adds two requirements beyond ordinary geometry: the bend must engage the longitudinal reinforcement, and the extension must project into the interior of the stirrup or hoop rather than outward. Not every 135-degree hook automatically satisfies these seismic detailing requirements; the engagement and projection conditions must be specifically detailed and verified.

Hook Detailing Dimensions: A, G, J, and H

Shop drawings and fabrication schedules commonly use lettered dimensions rather than writing out “straight extension” or “bend diameter” every time. Common conventions include A or G (an overall hook dimension measured to the outside of the bar), J (a secondary leg dimension on 180-degree hooks), H (an approximate overall height for some 135-degree details), D (inside bend diameter), and d_b (nominal bar diameter). These fabrication-specific dimensions are defined by CRSI, most currently in CRSI IPG5.1-2026, Bend Diameters, Measuring Points, and Fabrication Tolerances for Steel Reinforcing Bars, rather than directly by ACI 318-25. Any A/G/J/H values used on a specific project’s shop drawings should be checked against the current CRSI fabrication reference or the fabricator’s own bend schedule rather than assumed from a generic chart, since these overall dimensions depend on measuring-point conventions that can vary between references.

How Rebar Hook Dimensions Are Measured

Field or shop measurement of a hook is not as simple as running a tape around the curve.

Straight Extension

Measured from the point of tangency of the bend, where the curve ends and the straight bar begins, to the free end of the bar.

Inside Bend Diameter

Measured across the inside of the bend, at the mandrel or pin the bar was formed around, not the outside curve of the bent bar.

Overall A/G Dimension

Measured as an overall outside dimension on the fabricated piece, useful for checking a finished bar against a shop drawing without needing to isolate the bend and tail separately.

J and H Dimensions

Secondary dimensions used mainly on 180-degree and 135-degree details to describe the return leg or approximate overall height of the bent shape.

Measuring Points

CRSI IPG5.1-2026 specifically defines standardized measuring points for reinforcing bar fabrication, meaning where on the bent shape a dimension actually starts and ends. Using consistent measuring points matters because two different conventions can describe the same physical bar with different-looking numbers.

Hook Geometry vs Total Rebar Cut Length

The total physical length of a bent bar is not simply the straight leg plus the straight hook extension, because the bend itself contributes additional arc length, and fabrication length conventions follow standardized measuring points rather than a simple sum. Bar schedules used by fabricators account for bend allowances, deductions, and the specific measuring-point convention in use, which is why a detailer’s cut-length calculation and a simple straight-line addition of the visible dimensions will not always match. For the physical stock and cut-length side of reinforcement, see the Rebar Size Chart.

Hooked Rebar Development Length l_dh

l_dh does not equal l_ext. Hooked-bar development length is governed by ACI 318-25 Section 25.4.3 and depends on variables including yield strength f_y, concrete strength f′_c, bar diameter d_b, concrete density, coating, confinement, and hook location. ACI 318-25 revised the hooked-bar development equation and its modification factors relative to ACI 318-19. For the full calculation, worked examples, and current-code values, see the dedicated Rebar Development Length Chart, which covers l_dh in depth alongside straight-bar and compression development.

What Controls Hooked-Bar Development Length?

Bar Size and Grade

Larger bars and higher reinforcement grades (Grade 80, Grade 100) generally require longer hooked-bar development length, similar in principle to straight-bar development.

Concrete Strength and Density

Higher concrete compressive strength reduces required development length. Lightweight concrete requires a density modification factor, increasing the required length compared with normalweight concrete of the same strength.

Coating

Epoxy-coated hooked bars require a coating modification factor that increases development length compared with uncoated bars.

Cover and Confinement

Side cover and transverse reinforcement (ties, stirrups) crossing the potential splitting plane both affect the confinement terms in the ACI 318-25 hooked-bar equation.

Hook Location

Whether the hook is anchored within a confined column core or joint, versus elsewhere in the member, changes the applicable location-related modification factor.

Full calculation detail for each of these factors is covered on the Rebar Development Length Chart.

Hook Cover, Spacing, and Confinement

Hook anchorage performance depends heavily on the concrete surrounding the bend. Side cover affects the concrete’s resistance to splitting outward as the hook transfers load. Spacing between adjacent hooked bars affects how much concrete each hook can rely on before interacting with its neighbor. Ties and stirrups crossing the potential splitting plane provide measurable confinement credit in the ACI 318-25 hooked-bar equation. ACI 318-25’s anchorage revisions specifically address hooked-bar behavior and reinforcing-bar-group breakout checks. For cover and spacing values themselves, see the Concrete Cover Chart and the Rebar Grid Calculator.

Rebar Hooks by Structural Application

Footings and Foundations

Hooks anchor dowels and column starter bars into footings where straight embedment depth is limited by footing thickness.

Beams and Beam Ends

Hooks anchor longitudinal reinforcement at discontinuous beam ends and at beam-column joints where straight development would extend beyond the available member depth.

Columns and Dowels

Hooked dowels connect columns to footings or foundations, and hooks appear on column ties for confinement.

Walls

Hooks anchor wall reinforcement at wall ends, corners, and openings.

Beam-Column Joints

These are among the most demanding hook locations, often requiring specific seismic hook detailing in addition to ordinary anchorage requirements.

Stirrups, Ties, and Hoops

These transverse elements use the separate stirrup/tie hook geometry table covered earlier on this page, not the longitudinal end-hook table.

Hook type and anchorage method must follow the project’s specific design and detailing requirements. A statement like “footings always use 90-degree hooks” is not a reliable design rule; the engineer of record’s details govern.

Hook Orientation and Placement

Correct hook shape alone is not sufficient. Orientation and placement matter just as much as geometry: the direction the hook tail points, whether the hook actually engages the longitudinal reinforcement it is meant to confine, whether the hook sits inside the confined concrete core, actual cover at the hook location, placement tolerances, and reinforcement congestion in the immediate area. These placement details are especially important for ties, hoops, and seismic hooks, where engagement with the longitudinal bar and projection into the interior of the stirrup or hoop are explicit code requirements, not just good practice.

Fabrication Tolerances and Springback

Fabricated hook dimensions do not always equal a theoretical mathematical bend exactly, mainly because of springback, the tendency of steel to relax slightly after being bent around a mandrel or pin. The finished inside bend diameter, bar grade, coating, and the applicable fabrication tolerance all influence how closely a finished hook matches its nominal target dimension. CRSI IPG5.1-2026 is the current U.S. reference addressing bend diameters, measuring points, and fabrication tolerances for reinforcing bars, and it is the appropriate document to check for specific tolerance values on a given project rather than assuming zero tolerance on a theoretical chart dimension.

Hooks in Epoxy-Coated and Galvanized Rebar

Coated reinforcement raises two separate issues that should not be confused with each other.

Coatings can affect bending procedures and require specific handling to avoid damaging the coating during fabrication, and separately, epoxy coating increases the required hooked-bar development length under ACI 318-25. Do not assume the same fabrication dimensions or the same development-length modification automatically applies to every coated reinforcing system; galvanized-bar bend details in particular can differ from uncoated bar practice, so the applicable current coating and fabrication specification should be checked directly.

Standard Hook Worked Examples

ACI 318-25 and CRSI Rebar Hook Requirements

ACI 318-25 Section 25.3

Standard hooks, seismic hooks, crossties, and minimum inside bend diameters are governed by Section 25.3, covering Table 25.3.1 for longitudinal bars and Table 25.3.2 for stirrups, ties, and hoops.

ACI 318-25 Section 25.4.3

Development of standard hooks in tension, the structural anchorage calculation for hooked bars, is governed separately by Section 25.4.3.

CRSI Hook References

CRSI publishes field and shop reference materials covering 90-degree, 135-degree, and 180-degree hook fabrication details, commonly used alongside ACI 318 for detailing and shop-drawing dimensions.

CRSI IPG5.1-2026

CRSI IPG5.1-2026, Bend Diameters, Measuring Points, and Fabrication Tolerances for Steel Reinforcing Bars, is the current CRSI reference addressing exactly those three topics for current reinforcing bar grades.

ACI 318-19 vs ACI 318-25 Hook Provisions

This distinction matters in practice: an older ACI 318-19 hook geometry chart may still look familiar and largely usable, but an older ACI 318-19 hooked-bar development length table may no longer reflect current ACI 318-25 design values. Always confirm which code edition a reference chart or calculator is actually built on, and note that some adopted building codes, including some 2024 IBC-based jurisdictions, may still reference ACI 318-19 rather than ACI 318-25 until formally updated.

Common Rebar Hook Mistakes

Rebar Hook Length Chart Limitations

Rebar Hook Length FAQs

Related Calculators and Charts

This chart is a technical reference for standard rebar hook geometry based on ACI CODE-318-25, Building Code Requirements for Structural Concrete, and current CRSI fabrication guidance. It does not replace project-specific structural design, the engineer of record’s reinforcement details, or the building code edition and amendments adopted by the local jurisdiction.