Bolt Pull Out Force Calculator

Bolt Pull Out Force Calculator that compares thread stripping, bolt break, ACI 318 concrete breakout, epoxy bond and NDS wood withdrawal, then shows the weakest mode and its loads.

How a Bolt Pull Out Force Calculator Finds the Weak Link

A bolt pull out force calculator checks every way a loaded bolt can let go and reports the weakest one. For a bolt in a tapped hole or nut there are three: the bolt threads strip, the tapped threads strip, or the bolt snaps across its threads.

$$F_{pull}=\min (F_{boltstrip},F_{holestrip},F_{break})$$

The allowable load from a bolt pull out force calculator is that lowest value divided by a safety factor, often 2 for static loads. A well-designed joint has enough thread engagement that the bolt breaks first, because a broken bolt is easy to spot and replace while stripped threads in a part are not.

Worked Example: 1/2-13 Grade 5 Bolt in 6061 Aluminum

A 1/2-13 SAE Grade 5 bolt (120 ksi tensile strength) threads 0.750 in into 6061-T6 aluminum (42 ksi). With basic thread dimensions and shear strength taken as 0.577 × tensile strength, the bolt pull out force calculator gives three failure loads:

Failure Mode	Shear or Tensile Area	Strength Used	Failure Load
Bolt threads strip	0.7364 in²	69,240 psi	50,990 lbf
Aluminum threads strip	1.0308 in²	24,234 psi	24,981 lbf
Bolt breaks in tension	0.1419 in²	120,000 psi	17,028 lbf

The bolt breaks first at 17,028 lbf, so the allowable pull at a safety factor of 2 is 8,514 lbf. A 1,500 lbf service load uses 18% of that, and the aluminum threads would only strip if the bolt were somehow stronger than 24,981 lbf.

Bolt Pull Out Formula for Thread Stripping

Threads strip by shearing along a cylinder, and that geometry is the heart of every bolt pull out force calculator. The bolt's threads shear at the minor diameter of the tapped hole, and the hole's threads shear at the major diameter of the bolt, so each side has its own shear area per inch of engagement.

$$A_{s,bolt}=\pi K_n{L}_e\left[\frac{1}{2}+0.57735\frac{E_s-K_n}{P}\right]$$

$$A_{s,hole}=\pi D_s{L}_e\left[\frac{1}{2}+0.57735\frac{D_s-E_n}{P}\right]$$

K_n is the hole's minor diameter, E_s the bolt's pitch diameter, D_s the bolt's major diameter, E_n the hole's pitch diameter, P the pitch and L_e the length of full-thread engagement. These are the thread shear-area relations in FED-STD-H28/2, the same basis used by most thread stripping references.

$$F_{strip}=0.577\times F_u\times A_s$$

The 0.577 factor is 1/√3, the von Mises ratio of shear strength to tensile strength for ductile metals. Each side uses its own tensile strength, so in a bolt pull out force calculator the hole side in soft aluminum strips at a much lower load than the bolt side, even though its shear area is larger.

Basic Size vs Worst-Case Thread Fit

Basic dimensions give the nominal answer, which is the default in most bolt pull out force calculator tools. For a minimum-material check, use the Class 2A minimum bolt diameters and Class 2B maximum hole diameters, which shrink the shear areas and lower both strip forces by a few percent.

The Pitch Diameter Calculator gives E_s and E_n for any size, and the Thread Calculator gives the minor and major diameters.

Minimum Thread Engagement by Material

The shortest safe engagement is the length at which the weaker set of threads just matches the bolt's tensile strength. Any engagement past that point leaves the bolt as the weak link, which is the main design answer a steel bolt pull out force calculator gives.

$$L_{e,min}=\frac{F_u\times A_t}{0.577\times F_{u,weak}\times A_{s,weak}/L_e}$$

The chart below runs that bolt pull out force calculator math for three common bolts. Lengths are full threads only, so add the chamfer at the hole entry and any incomplete thread at the bottom of a blind hole.

Tapped Material (Tensile)	1/2-13 Grade 5	1/2-13 Grade 8	M10 Class 8.8
304 stainless (75 ksi)	0.286 in (0.57 × D)	0.358 in (0.72 × D)	5.7 mm (0.57 × D)
A36 steel (58 ksi)	0.370 in (0.74 × D)	0.463 in (0.93 × D)	7.3 mm (0.73 × D)
6061-T6 aluminum (42 ksi)	0.511 in (1.02 × D)	0.639 in (1.28 × D)	10.1 mm (1.01 × D)
5052-H32 aluminum (31 ksi)	0.693 in (1.39 × D)	0.866 in (1.73 × D)	13.7 mm (1.37 × D)
Class 30 gray iron (30 ksi)	0.716 in (1.43 × D)	0.895 in (1.79 × D)	14.1 mm (1.41 × D)

The familiar rule of 1 × D in steel and 2 × D in aluminum comes from this kind of math with margin added. A stronger bolt needs more engagement, not less: a Grade 8 bolt in 5052 aluminum needs 1.73 × D before it breaks ahead of the threads.

Gray iron is brittle and its shear strength is not well described by 0.577 × tensile, so treat the iron row as a conservative estimate. A standard nut of the same grade as the bolt needs only about 0.5 × D of engagement, which is why a full-height nut is always stronger than the bolt.

Bolt Pull Out Strength Chart by Engagement

Strip force rises in a straight line with engagement, while the bolt's breaking load stays fixed, so a bolt pull out force calculator can show exactly where the two cross. This chart shows the tapped-thread strip force for a 1/2-13 Grade 5 bolt in two materials, against its 17,028 lbf breaking load.

Engagement	Ratio to D	Strip Force, 6061-T6 Aluminum	Strip Force, A36 Steel	Fails First (Aluminum)
0.250 in	0.50 × D	8,327 lbf	11,499 lbf	Tapped threads
0.375 in	0.75 × D	12,491 lbf	17,249 lbf	Tapped threads
0.500 in	1.00 × D	16,654 lbf	22,998 lbf	Tapped threads
0.750 in	1.50 × D	24,981 lbf	34,498 lbf	Bolt breaks
1.000 in	2.00 × D	33,308 lbf	45,997 lbf	Bolt breaks

At 1 × D in 6061, the aluminum strips at 16,654 lbf, just under the bolt's 17,028 lbf. That narrow margin is why 1.5 × D is a common design choice in aluminum and 1 × D in steel.

Anchor Bolt Pull Out Strength in Concrete

A bolt pull out force calculator for concrete follows ACI 318-19 Chapter 17. A cast-in anchor has three tension failure modes: the steel rod breaks, a cone of concrete breaks out, or the head pulls through the concrete it bears on.

$$N_{sa}=A_{se}{f}_{uta}$$

$$N_b=24{\lambda }_a\sqrt{f_c^{\prime }}{h}_{ef}^{1.5}$$

$$N_p=8A_{brg}{f}_c^{\prime }$$

A_se is the tensile stress area, f_uta the rod's tensile strength (capped at 1.9 × yield and 125 ksi), h_ef the effective embedment and A_brg the net bearing area of the head or nut. Each is multiplied by its own φ factor: 0.75 for ductile steel, and 0.70 for breakout and pullout without supplementary reinforcement.

Pullout Strength of a 3/4 in Anchor Bolt

A 3/4 in ASTM F1554 Grade 36 rod with a heavy hex nut, embedded 8 in in 4,000 psi cracked concrete far from any edge, has a design strength of 14,549 lbf. The steel governs; breakout gives 24,042 lbf and head pullout 20,415 lbf after their φ factors.

Run the bolt pull out force calculator again at 4 in of embedment and breakout takes over at 8,500 lbf. Move it 6 in from an edge at 8 in deep and breakout falls from 34,346 lbf to 21,896 lbf nominal, though the steel still governs.

Concrete Bolt Pull Out Chart

Design tension strength φN_n for single F1554 Grade 36 anchors with heavy hex nuts, in 4,000 psi cracked concrete, with edges at least 1.5 × h_ef away. The letter shows what governs: S for steel, B for breakout.

Anchor	4 in Embed	6 in Embed	8 in Embed	10 in Embed	Embed for Steel to Govern
1/2 in	6,173 lbf (S)	6,173 lbf (S)	6,173 lbf (S)	6,173 lbf (S)	3.2 in
5/8 in	8,500 lbf (B)	9,831 lbf (S)	9,831 lbf (S)	9,831 lbf (S)	4.4 in
3/4 in	8,500 lbf (B)	14,549 lbf (S)	14,549 lbf (S)	14,549 lbf (S)	5.7 in
7/8 in	8,500 lbf (B)	15,616 lbf (B)	20,086 lbf (S)	20,086 lbf (S)	7.1 in
1 in	8,500 lbf (B)	15,616 lbf (B)	24,042 lbf (B)	26,350 lbf (S)	8.5 in

Breakout does not depend on bolt size, only on embedment and concrete strength, which is why every anchor shows 8,500 lbf at 4 in. A bigger anchor only pays off with deeper embedment, so the last column is a useful bolt embedment depth calculation.

Uncracked concrete raises breakout by 1.25 and pullout by 1.4 for cast-in anchors. In Seismic Design Categories C through F, ACI 318 multiplies the concrete modes, but not the steel, by 0.75: the 3/4 in anchor at 4 in drops from 8,500 lbf to 6,375 lbf.

For deep cast-in anchors between 11 and 25 in, ACI permits N_b = 16√f′c × h_ef^5/3, which beats the h_ef^1.5 form above about 11.4 in. At 12 in that gives 63,648 lbf nominal breakout. Anchor groups and anchors near three or four edges need ACI's group equations, which a single-anchor check does not cover.

Epoxy Anchor Pull-Out Force

An epoxy anchor needs a different bolt pull out force calculator path. An adhesive anchor fails when the bond between the epoxy, the rod and the concrete lets go. ACI 318 treats the bond as a uniform stress over the rod's embedded surface.

$$N_{ba}={\lambda }_a\tau \pi d_a{h}_{ef}$$

τ is the characteristic bond stress, d_a the rod diameter and h_ef the embedment, which ACI limits to between 4 and 20 rod diameters. The design strength then takes φ by anchor category: 0.65, 0.55 or 0.45 for categories 1 to 3 without supplementary reinforcement, rising to 0.75, 0.65 or 0.55 with it (Condition A).

The bond stress you enter in a bolt pull out force calculator should come from the adhesive's ICC-ES evaluation report. When no report is used, ACI 318 sets low minimum values: 300 psi cracked and 1,000 psi uncracked indoors, and 200 psi cracked and 650 psi uncracked outdoors.

Those minimums are deliberately cautious. A 5/8 in rod set 6 in deep in cracked concrete reaches only 3,534 lbf nominal and 2,297 lbf design strength at the indoor minimum, against 9,831 lbf for the steel. Product values in an evaluation report are usually several times higher.

Adhesive anchors also check concrete breakout with k_c = 17 instead of 24, since post-installed anchors break out at lower loads than cast-in ones. The Bolt Length Calculator sizes the rod length above the concrete for the fixture, washer and nut.

Screw Pull Out Force in Wood

A screw pull out force calculator for wood uses withdrawal values, not thread shear. Lag screws and wood screws resist withdrawal by gripping wood fibers along their threads. The NDS gives reference withdrawal values per inch of thread penetration, set by the wood's specific gravity G and the screw diameter D.

$$W_{lag}=1800G^{1.5}{D}^{0.75}$$

$$W_{screw}=2850G^{2}D$$

W is in pounds per inch of thread in the main member. The wood screw equation matches the NDS form in Huber Engineered Woods' fastener withdrawal note, which applies the load duration and wet service factors the same way.

Example: a 1/2 in lag screw with 3 in of thread in Douglas Fir-Larch (G = 0.50) has W = 378 lb per inch, or 1,135 lbf allowable for normal load duration. An 800 lbf load needs at least 2.11 in of thread penetration.

Adjustment	Factor	1/2 in Lag, 3 in Penetration
Normal load (CD)	1.00	1,135 lbf
Wind or seismic (CD)	1.60	1,816 lbf
Wet service (CM)	0.70	795 lbf
End grain, lag only (Ceg)	0.75	851 lbf

The NDS does not allow wood screws to be loaded in withdrawal from end grain, so end-grain connections need lag screws or a different detail. Denser species help a lot: Red Oak at G = 0.67 holds about 55% more per inch than Douglas Fir-Larch for a lag screw.

Bolt Pull Through Calculation

Pull-through is the opposite failure: the bolt head or washer punches through a thin plate or sheet instead of the threads letting go. It governs in sheet metal, thin brackets and soft plastics, so run it alongside the bolt pull out force calculator whenever the clamped part is thin.

$$F_{pt}\approx \pi d_{w}t{\tau }_s$$

d_w is the bearing diameter of the head or washer, t the sheet thickness and τ_s its shear strength. A 1/2 in bolt with a 1.062 in washer on 1/8 in 5052-H32 aluminum, at τ_s = 0.577 × 31 ksi, pulls through at 7,460 lbf, well below the bolt's 17,028 lbf breaking load.

Plate Thickness	Pull-Through, 1.062 in Washer	Allowable at Ω 2	Fails First
0.125 in	7,460 lbf	3,730 lbf	Plate
0.188 in	11,190 lbf	5,595 lbf	Plate
0.250 in	14,919 lbf	7,460 lbf	Plate
0.313 in	18,649 lbf	8,514 lbf	Bolt
0.375 in	22,379 lbf	8,514 lbf	Bolt

The crossover is at 0.285 in of 5052 for the washer, so plates thinner than about 9/32 in let the head pull through before a Grade 5 bolt breaks. Without the washer, the 3/4 in hex head alone pulls through at 5,268 lbf and needs 0.404 in of plate.

A larger washer raises pull-through in direct proportion to its diameter; keeping the 1/8 in plate would take a 2.42 in washer to make the bolt the weak link. The Punch Force Calculator uses the same perimeter-times-thickness shear relation for punching holes.

How to Calculate Force on Bolts

The load you enter in a bolt pull out force calculator is the force on one bolt: the total tension divided by the number of bolts, plus any extra from prying or eccentric loads. Four bolts holding a 4,000 lb hanging load each carry 1,000 lbf if the load is centered.

To find bolt force from torque, use the nut factor: F = T ÷ (K × D). A 1/2-13 bolt at 50 ft-lb (600 in-lb) with K = 0.20 clamps at 600 ÷ (0.20 × 0.5) = 6,000 lbf. The Bolt Preload Calculator and Bolt Friction Coefficient Calculator refine that number.

Preload matters for pull-out because tightening loads the threads before any service load arrives. A tapped joint should carry the preload plus the external load share without stripping, so check strip force against the bolt's full tensile strength rather than the service load alone.

Bolt Pull Out Force Calculator in Excel

A bolt pull out force calculator in Excel needs the hole-side strip force and the bolt break load. With diameter in B1, TPI in B2, engagement in B3, tapped material tensile strength in B4 and bolt tensile strength in B5:

=0.577*B4*PI()*B1*B3*(0.5+0.57735*0.649519)
=B5*PI()/4*(B1-0.974279/B2)^2

The first line is the tapped-thread strip force with basic dimensions, because (D - E_n) ÷ P is always 0.6495 for basic 60° threads. For 0.5, 13, 0.75, 42,000 and 120,000 it returns 24,981 lbf and 17,028 lbf, matching the worked example.

Pull Force, Units and Bolt Basics

A pull-out check sits next to everyday force questions: how loads are measured, what a newton is, and how static strength relates to vibration and odd materials.

What is a bolt pull out force calculator?

It is a tool that compares every tension failure mode of a fastener, such as thread stripping, bolt fracture, concrete breakout or wood withdrawal, and reports the lowest load as the pull-out strength. The result tells you both the capacity and which part gives way first.

How do you calculate pull out strength?

Work out each failure load separately, then take the smallest. For a tapped hole, that is 0.577 × tensile strength × thread shear area for each thread set, against tensile strength × stress area for the bolt; for concrete, it is the ACI 318 steel, breakout and pullout values with their φ factors.

What is bolt pull out force?

Bolt pull out force is the axial load that pulls a bolt or anchor free of the material holding it, and it is what a bolt pull out force calculator solves for, by stripping threads, breaking out concrete or tearing wood fibers. If the bolt itself snaps first, that breaking load is the joint's real pull-out limit.

Why is calculating bolt pull-out strength important?

A bolt pull out force calculator tells you which part fails and at what load. Stripped threads in an aluminum housing or a concrete breakout are expensive to repair, while a bolt that breaks first is cheap to replace, so the check is how you design for the safer failure.

How is pull force measured?

On site, a hydraulic pull tester with a calibrated gauge loads the anchor in tension until a proof load or failure. Laboratory tests for concrete anchors follow ASTM E488, and threaded joints are tested in a tensile machine with the tapped part clamped.

How do you calculate a pulling force?

Pulling force is mass times acceleration, F = m × a. To hold a hanging load still, the force equals its weight, m × g: a 100 kg load needs 981 N, or about 220 lbf, shared among the bolts holding it.

How much is 5 newtons of force?

Five newtons equals 1.12 lbf, about the weight of a 510 g (1.1 lb) mass on Earth. Bolt pull-out loads are usually thousands of newtons, so results are often given in kN, where 1 kN = 224.8 lbf.

What is the formula for bolt strength?

Bolt tensile strength is F = F_u × A_t, the material's tensile strength times the tensile stress area. A 1/2-13 Grade 5 bolt gives 120,000 × 0.1419 = 17,028 lbf; the Bolt Area Calculator gives A_t for any size.

How do you calculate bolt weight?

Multiply volume by density, 0.2836 lb/in³ for steel. A 1/2 × 3 in hex bolt has about 0.589 in³ of shank and 0.168 in³ of head, so it weighs about 0.21 lb before subtracting the small volume lost to threads.

Can a bolt pull out force calculator be used for dynamic loads?

A bolt pull out force calculator gives static strength. For vibration or cyclic loads, use a higher safety factor of 3 to 4 and keep the bolt properly preloaded, since fatigue of the first engaged thread, not static stripping, usually ends a dynamically loaded joint.

Can I use it for non-standard bolt sizes and materials?

Yes, any diameter and pitch works with the shear-area equations, and any tapped material works if you know its tensile strength. For plastics and composites, use tested pull-out data instead, because their shear behavior does not follow the 0.577 rule.

What should I do if the results seem off?

Check units first, especially ksi versus psi, and inches versus millimeters if you use the bolt pull out force calculator in metric. Then check that engagement counts only full threads, and that the tapped material strength matches its temper: 6061-T6 is more than twice as strong as annealed 6061-O.