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Anchor Bolt Calculator — Embedment, Pullout & Projection

Cast-in-place anchor screening in one screen: concrete breakout tension from the ACI 318 cone model, F1554 rod capacity in tension and shear, the projection that sticks out above the slab, and a J-bolt weight estimate — with cracked/uncracked concrete and four installation scenarios.

Input Parameters

Unit System
Installation Scenario
Concrete f′c
MPa
Embedment h_ef
mm
Anchor Rod
Concrete Condition

Cracked is the default for seismic, dynamic loads, and tension zones — assume cracked unless the design proves otherwise.

Grout / Leveling Pad above slab, under nut
mm

Concrete Breakout Tension (nominal)

184.8 kN

N_cb = 17 · √f′c · h_ef^1.5

Steel Rod Tension (nominal)

81.2 kN

N_sa = As · Fu (Gr55)

Governing capacity

81.2 kN

Steel rod governs

Detailing breakdown

Nominal shear capacity (0.45·Fu·As, threads not excluded)36.5 kN
Breakout cone depth ≈ h_ef300 mm
Minimum edge distance cNa ≈ 1.5·h_ef450 mm
Minimum spacing ≈ 3·h_ef (full cone each)900 mm
Projection above slab (grout + nut + washer + 1.5d)66.8 mm
Total rod length (embed + hook + projection)366.8 mm
Rod weight (⌀ M16)0.58 kg
Reference

ASTM F1554 Anchor Rod Grades

F1554 is the default anchor rod specification for structural and equipment work in North America: three yield grades, weldable supplement (S) available, and straight, L-shaped, or bent (J) configurations from the same chemistry.

GradeYield MPa (ksi)Tensile MPa (ksi)Typical EmbedmentTypical Projection
Gr36248 (36)400 (58)12d≈ 2d + grout + nut
Gr55380 (55)517 (75)12d≈ 2d + grout + nut
Gr105724 (105)862 (125)15d≈ 2d + grout + nut

Embedment figures are typical hardware defaults (12d for Gr36/55, 15d for the stronger Gr105), not code minimums — the ACI cone model with your actual loads governs. Projection includes the grout pad, heavy hex nut, and washer.

Weights

J & L Anchor Nominal Weights

Straight-rod weights from the 7850 kg/m³ steel density — close enough for freight, material takeoffs, and cost checks, and the same math the calculator’s weight output runs.

Rod Ø (mm)kg/mlb/ft (equiv.)400 mm straight length (kg)J-bolt with hook (~kg)
M120.8880.60.360.41
M161.581.060.630.76
M202.471.660.991.24
M243.552.391.421.85
M305.553.732.223.05

Hook allowance ≈ 5×d of extra rod consumed by the bend. Actual foundry pieces vary with bend radius and thread run-out — treat as ±10%.

The Big Picture

The Five Failure Modes ACI 318 Chapter 17 Makes You Check

An anchor bolt design is finished when all five modes are cleared — not when the first number looks comfortable. This calculator models two of the five directly (steel fracture and breakout); the flags mark where the rest live.

Steel rod fracture

Modeled here

The rod itself yields and breaks at the threads. This is the ductile, predictable mode every seismic detail tries to force.

Concrete breakout cone

Modeled here

A cone of concrete pulls out with the anchor — the k·√f'c·he^1.5 model, truncated by edges and neighbor anchors.

Pullout / bond

Code check

The anchor slides straight out of its hole — governed by head bearing or adhesive bond. Epoxy capacities live here.

Side-face blowout

Code check

An anchor close to a free edge blows a wedge of concrete sideways under tension. Edge distance cNa ≈ 1.5he is the first screening rule.

Concrete pyrout (shear)

Code check

Under shear, a shallow anchor pries a spall out of the surface. Deep embedment and stiff base plates suppress it.

Nominal capacities are shown without design (φ) factors — applying the code’s φ, the load combinations, and the five-mode sweep is what turns this screen into a signed design. Use it to understand the mechanics and sanity-check numbers, then run the actual code path on a governed project.

Detailing

Anchor Bolt Projection: What Sticks Out Above the Slab

Projection is where anchoring meets assembly. The stack above the concrete is grout pad + nut height + washer + thread that must still bite: the working rule is 1.5×d of usable thread beyond the grout line, so an M16 on a 25 mm pad projects about 67 mm and a 3/4-inch rod on a 1-inch pad about 2-3/4 inches.

Too little projection and the base plate cannot be leveled — the nut runs out of thread before the shims do. Too much and the exposed thread costs real money: galvanized thread exposure corrodes first, thread protectors get ordered by the hundred, and on rotating-equipment bases the excess catches coupling guards and safety walks. Equipment-base details typically land projection at 2d + grout; pole bases run taller pads and correspondingly taller sticks.

The grout pad itself is a design element, not slack: non-shrink grout from 25 to 75 mm transfers the base plate bearing into the slab, and its edge must not be thinner than the bolt spacing rules assume. When a detail shows projection measured “from top of concrete” but the grout is placed after anchor set, someone re-measures everything — measure from the grout surface, order rods with the pad included.

Projection stack, M16 on 25 mm grout

Grout pad25 mm
Heavy hex nut (M16)14.8 mm
Washer3 mm
Usable thread 1.5×d24 mm
Total projection≈ 67 mm

Template tip: set anchor bolts against a steel template locked to the formwork — free-hand setting drifts past the tolerance of every base plate hole ever drilled, and the bolt circle calculator gives the template’s X/Y layout when the pattern is circular.

Scenarios

Four Installation Scenarios, Four Judgment Calls

Equipment bases — pumps, motors, skids

The classic four-anchor pattern on a grouted base plate. Capacity is rarely the binding constraint; template accuracy and projection are. Check the breakout cone against the pad's edge distance — pump pads are small, and a 300 mm embedment with a 150 mm edge is already truncating the cone. Vibration-loaded bases (pumps, compressors) belong in the cracked-concrete assumption regardless of code minimums.

Light poles and signs — overturning moment

A pole base puts one side of the anchor circle in heavy tension while the other side compresses. Embedment follows the moment, not the rod: 12d is the hardware floor, real pole piers run 300–600 mm. The cage of 4–8 J-bolts on a template ring behaves as an anchor group — the group cone, not the single-anchor cone, is the honest model, and this calculator's single-anchor number is the per-bolt ceiling.

J and L anchors — the bent-rod classics

The hook's job is mechanical interlock for pre-code construction and lightly loaded foundations; modern code capacity still runs through the cone and steel modes, with the hook providing anchorage at the embedment end. Add the hook's rod length (about 5d for a J, 8d for an L) to the material takeoff — it is real steel that never shows up in the projection.

Chemical (epoxy) anchors — the ESR rule

Post-installed adhesive anchors get their capacity from the manufacturer's ICC-ES report: hole diameter, cleaning, cure temperature, and seismic qualification are all part of the published value. The cone and steel math here still bounds the problem — concrete cannot magically exceed its breakout, and the rod cannot exceed its steel — but the adhesive layer is the difference between two epoxies of the same rod size performing 2:1. No generic table replaces the ESR; this tool refuses to pretend otherwise.

FAQ

Anchor Bolt FAQ

Capacity, embedment, projection, and the code boundary — the questions this calculator exists to answer.

How is anchor bolt capacity calculated in concrete?
Concrete capacity follows the breakout cone model from ACI 318 Chapter 17: the nominal tension capacity Ncb = k·√f'c·he^1.5, where k is 17 for cracked concrete and 24 for uncracked, f'c is the compressive strength and he the effective embedment. A 300 mm embedment in 25 MPa concrete works out to about 185 kN (41,600 lbf) nominal per anchor before any edge, spacing, or design factors — but the steel rod itself may govern first, and whichever is smaller is the honest answer.
What is the F1554 anchor bolt capacity for a Gr55 rod?
Steel tension capacity is the thread stress area times the tensile strength: an F1554 Gr55 rod (Fu = 517 MPa / 75 ksi) at M16 gives 157 mm² × 517 MPa ≈ 81 kN (18,300 lbf) nominal. Capacity in the code sense then applies a design factor to whichever governs — steel or concrete breakout — which is why two calculators quoting the 'same' anchor can differ by 40% and both be right.
How deep should a light pole anchor bolt be embedded?
Light pole and sign foundations typically land at 12× the rod diameter as a minimum embedment — an M16/F1554 Gr55 pole base starts around 190 mm of embedment and most real details run 300–600 mm into the pier, governed by the overturning moment rather than the anchor cone. Taller poles, higher wind zones, or crane-like loads push the design to the foundation engineer; the 12d value is a hardware floor, not a wind-load answer.
How do you calculate anchor bolt projection above the slab?
Projection = leveling grout thickness + nut height + washer thickness + thread run-out, with 1.5×d of usable thread as the working rule so the equipment base plate seats on the nut with margin for shims. An M16 on a 25 mm grout pad projects about 25 + 14.8 + 3 + 24 ≈ 67 mm. Too little projection and the nut bottoms; too much and the exposed thread is a corrosion and snagging liability.
What spacing do anchor bolts need from each other and from edges?
The breakout cone wants room: center-to-center spacing near 3×he and edge distance around 1.5×he let each anchor develop the full cone without overlap — the cNa ≈ 1.5he edge rule. Closer spacing or thinner edges are perfectly workable but each anchor's cone gets truncated and the concrete capacity drops proportionally. Pump bases with bolts 200 mm apart on 300 mm embedment are running at roughly two-thirds of the single-anchor number.
How much does a J-bolt anchor weigh?
Straight-rod math is close enough for shipping and cost estimates: weight = rod cross-section × 7850 kg/m³ × length. An M20 J-bolt with 400 mm of rod is about 0.99 kg before the hook — and the J or L hook adds real length: a standard J on M20 consumes roughly 80–120 mm of extra rod depending on the bend radius. The calculator's weight estimate includes a hook allowance you can see in the breakdown.
Do seismic requirements change anchor bolt design?
Yes, materially. Seismic design categories above A require anchors to handle tension with ductility — either the steel governs (ductile rod failure) or the concrete side gets overstrength load factors. ACI 318 Chapter 17 adds pullout and concrete-side checks for seismic, and cracked-concrete assumptions become mandatory for most connections. This calculator's cracked/uncracked toggle is the first-order version of that conversation, not the whole code path.
Can this calculator size epoxy (chemical) anchors?
No — and no generic calculator should. Post-installed epoxy anchor capacities come from the manufacturer's ICC-ES/ESR report, which encodes the specific adhesive, hole diameter, cleaning procedure, installation temperature, and cracked-concrete qualification. Use the concrete and steel numbers here as a reality check on what order of capacity to expect, then read the ESR table for the actual design values. In California and other high-seismic jurisdictions, the ESR's seismic qualification (Option 1, AC308) is a purchase requirement, not a preference.
What f'c should I use for a pump or equipment foundation?
Most equipment pads are specified at 25–35 MPa (3600–5000 psi) at 28 days. Use the specified value, not the early-age value — anchors are usually torqued at 7 days when concrete is at maybe 70% of spec, and the breakout formula scales with √f'c, so early tightening on a 25 MPa pad behaves like a 17 MPa pad. If the schedule forces early anchor torque, derate or wait; the concrete does not care about the project schedule.
How is stress checked on crane rail and machine base anchor bolts?
Crane and press anchors see fatigue: the tension cycle from every lift or stroke works the threads thousands of times. The static calculation here sets the ceiling, but fatigue design keeps the working tension well under the yield-proportional preload and prefers longer, more compliant anchors that soften the load cycle. If the load cycles, treat this calculator's number as the first screening step and hand the fatigue question to a specialist — that is exactly the kind of judgment the five failure modes exist to force.

Anchor the Base, Then Spec the Rest of the Joint

This anchor bolt calculator covers the concrete side of the connection; the fastener side lives on the homepage’s free bolt torque calculator — torque, preload, and the strength check for the grade — and the bolt calculators hub rounds out shear, length, weight, and bolt circles. One standards-first toolset from the embedment cone to the final wrench click.

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