Anchor Bolt Size and Capacity Chart

Anchor bolt sizes from 1/2 to 2 inches: their dimensions, steel strength in each ASTM F1554 grade, and how much tension a single bolt holds in concrete at embedments of 4 to 18 inches.

The strengths are design strengths (φN_n and φV_n, in kips) under ACI 318-19 Chapter 17, from the same calculations as the free anchor bolt designer. Compare them with factored (LRFD) loads.

Anchor bolt size chart

Diameter	Threads per inch	Tensile stress area, A_se	Heavy hex nut bearing area, A_brg
1/2 in	13	0.142 in²	0.467 in²
5/8 in	11	0.226 in²	0.671 in²
3/4 in	10	0.334 in²	0.911 in²
7/8 in	9	0.462 in²	1.188 in²
1 in	8	0.606 in²	1.501 in²
1-1/8 in	7	0.763 in²	1.851 in²
1-1/4 in	7	0.969 in²	2.237 in²
1-3/8 in	6	1.16 in²	2.659 in²
1-1/2 in	6	1.41 in²	3.118 in²
1-3/4 in	5	1.9 in²	4.144 in²
2 in	4.5	2.5 in²	5.316 in²

A_se is the area the threads leave to carry tension. A_brg is the area of a heavy hex nut (or head) bearing on the concrete, less the rod, which sets the pullout strength.

Anchor bolt steel strength by grade

ASTM F1554 is the usual specification for anchor rods. Grade 36 is the most common; grades 55 and 105 are stronger but no stiffer, and only help where the steel, not the concrete, governs.

Design steel strength, kips: φN_sa = 0.75 A_se f_uta and φV_sa = 0.65 × 0.6 A_se f_uta
Diameter	Gr. 36 tension	Gr. 36 shear	Gr. 55 tension	Gr. 55 shear	Gr. 105 tension	Gr. 105 shear
1/2 in	6.2	3.2	8.0	4.2	13.3	6.9
5/8 in	9.8	5.1	12.7	6.6	21.2	11.0
3/4 in	14.5	7.6	18.8	9.8	31.3	16.3
7/8 in	20.1	10.5	26.0	13.5	43.3	22.5
1 in	26.4	13.7	34.1	17.7	56.8	29.5
1-1/8 in	33.2	17.3	42.9	22.3	71.5	37.2
1-1/4 in	42.2	21.9	54.5	28.3	90.8	47.2
1-3/8 in	50.5	26.2	65.2	33.9	108.7	56.6
1-1/2 in	61.3	31.9	79.3	41.2	132.2	68.7
1-3/4 in	82.6	43.0	106.9	55.6	178.1	92.6
2 in	108.8	56.6	140.6	73.1	234.4	121.9

Minimum tensile strength f_uta: grade 36, 58 ksi; grade 55, 75 ksi; grade 105, 125 ksi. The shear values are for a bolt bearing directly on the base plate, with no grout pad.

Anchor bolt tension capacity by embedment

A bolt in tension can fail three ways: the steel breaks, a cone of concrete breaks out around it, or the nut pulls through the concrete. The table gives the lowest of the three for an F1554 grade 36 rod with a heavy hex nut at its embedded end, in 3,000 psi concrete.

Design tension strength φN_n, kips, by embedment h_ef
Diameter	4 in	6 in	8 in	10 in	12 in	15 in	18 in
1/2 in	6.2	6.2	6.2	6.2	6.2	6.2	6.2
5/8 in	7.4^b	9.8	9.8	9.8	9.8	9.8	9.8
3/4 in	7.4^b	13.5^b	14.5	14.5	14.5	14.5	14.5
7/8 in	7.4^b	13.5^b	20.0^p	20.0^p	20.0^p	20.0^p	20.0^p
1 in	7.4^b	13.5^b	20.8^b	25.2^p	25.2^p	25.2^p	25.2^p
1-1/8 in	7.4^b	13.5^b	20.8^b	29.1^b	31.1^p	31.1^p	31.1^p
1-1/4 in	7.4^b	13.5^b	20.8^b	29.1^b	37.6^p	37.6^p	37.6^p
1-3/8 in	7.4^b	13.5^b	20.8^b	29.1^b	38.6^b	44.7^p	44.7^p
1-1/2 in	7.4^b	13.5^b	20.8^b	29.1^b	38.6^b	52.4^p	52.4^p
1-3/4 in	7.4^b	13.5^b	20.8^b	29.1^b	38.6^b	56.0^b	69.6^p
2 in	7.4^b	13.5^b	20.8^b	29.1^b	38.6^b	56.0^b	75.8^b

Unmarked values are limited by the steel, ^b by concrete breakout and ^p by pullout.
One bolt, at least 2 h_ef from any edge and from other bolts, in cracked concrete with no reinforcement to hold the breakout cone. Closer edges and bolt groups lower the breakout strength; the anchor bolt designer works them out.
Breakout grows with √f′_c: in 4,000 psi concrete it's 15% higher, and pullout is a third higher.
Not for seismic design categories C to F, which add their own requirements (ACI 318-19 17.10).

For example, a 3/4 in rod embedded 12 in holds 14.5 kips: its steel gives 14.5, pullout 15.3 and breakout 38.6. Embedding it deeper than about 8 in gains nothing, because the steel already governs.

How long should an anchor bolt be?

Add the embedment to everything the bolt passes through above the concrete, plus a little thread to spare:

length = embedment + embedded nut + grout + base plate + washer + nut + 2 to 3 threads

For a 3/4 in rod with 12 in of embedment, a 3/4 in heavy hex nut at the bottom, 1-1/2 in of grout, a 3/4 in base plate, a 1/4 in plate washer and a 3/4 in nut on top, that's 16 in, plus 1/2 in of thread: 16.5 in. Round up to an 18 in rod. A heavy hex nut is about as tall as the rod is wide.

Anchor bolts for house sill plates

For a wood-framed house, the International Residential Code (IRC) section R403.1.6 sets the usual sill plate anchor bolts: at least 1/2 in diameter, embedded at least 7 in into the concrete or grouted masonry, no more than 6 ft apart, with at least two bolts in each piece of plate and one within 12 in of each end (but no closer than seven bolt diameters). A 1/2 × 10 in bolt is the common choice. Higher wind and seismic areas need more; check with the local building department.

Anchor bolt questions

What size anchor bolt do I need?

Enough to carry the factored tension and shear on each bolt. Column base plates commonly use 3/4 in rods, and OSHA requires at least four for most steel columns. A 5/8 in rod embedded 6 in holds 9.8 kips; a 1 in rod embedded 10 in holds 25.2 kips.

Does a deeper anchor bolt hold more?

Up to a point. Breakout strength grows with embedment to the power of 1.5, so a deeper bolt pulls a bigger cone of concrete. Once the cone is stronger than the steel or the nut's bearing, more depth doesn't help.

What's the difference between grade 36, 55 and 105?

Their strength: F1554 grade 36 rods have a minimum tensile strength of 58 ksi, grade 55 of 75 ksi and grade 105 of 125 ksi. Grade 55 rods are often specified as weldable (supplement S1). Most rods are color coded on the projecting end: blue for 36, yellow for 55 and red for 105.