Foundation Bolt Weight Chart and Calculation (M12 to M36)

A J bolt or L bolt is a steel rod bent at one end and threaded at the other. To find its weight, work out the straight length of bar, multiply by the weight per metre and take off a little for the thread. This guide gives bar weights from M12 to M36, the length formulas and two worked examples.

Foundation Bolt Weight per Metre, M12 to M36

Steel at 7.85 g/cm³. The threaded part has a coarse metric thread to ISO 261 (see our thread pitch chart).

How to read the chart: the plain bar weight is π/4 x d² x 7.85 / 1000 kg per metre, with d in mm, or about d x d / 162. It matches the nominal bar masses in IS 1786 and EN 10080, such as 0.888 kg for 12 mm. The thread allowance is how much lighter 100 mm of thread is than 100 mm of plain bar.

Inch (BSW) bolts: use the bar diameter in mm. 5/8″ bar weighs 1.55 kg, 3/4″ 2.24 kg and 1″ 3.98 kg per metre. For the thread allowance, use the nearest metric size as a guide.

How to Find the Straight Length of a J Bolt or L Bolt

A bent bolt is made from a straight bar. Measure it along the centre line of the rod. Straight parts count at full length. A bend counts as an arc of radius R, which is the inside bend radius plus d/2. A 90 degree bend is 1.5708 x R long and a half turn is 3.1416 x R.

• L bolt: L is the overall length, from the top of the thread to the underside of the bend. B is the leg length, from the outside of the rod to the end of the leg. r is the inside bend radius. Straight length = L + B − 2 x (r + d) + 1.5708 x (r + d/2).
• J bolt: L is the overall length, from the top of the thread to the bottom of the hook. W is the outside width of the hook. The hook radius is R = (W − d) / 2. Straight length = L − R − d/2 + 3.1416 x R, plus any straight tail.

If your drawing measures the hook or leg another way, use the centre line in the same way. As a quick check, an L bolt with an inside radius of 1d to 4d needs about L + B minus 1.6d to 2.9d.

How Much Lighter the Threaded Part Is

We take the threaded part as a rod of the pitch diameter, d minus 0.6495 x pitch, the same method as our hex bolt weight chart. The results agree with published DIN 975 threaded rod weights within about 1 % for most sizes, such as 2.08 kg per metre for M20.

100 mm of M20 thread is 38.4 g lighter than plain bar, about 2 % of a 600 mm J bolt.

J Bolt Weight Example: M20, 600 mm with 100 mm Wide Hook

Steel, 600 mm overall, hook 100 mm wide outside with no tail, 100 mm of thread.

1. Hook radius: R = (100 − 20) / 2 = 40 mm.
2. Straight length = 600 − 40 − 10 + 3.1416 x 40 = 675.7 mm.
3. Plain bar weight = 0.6757 m x 2.466 kg per metre = 1.666 kg.
4. Thread allowance: 100 mm of M20 thread = 0.038 kg.
5. Bolt weight = 1.666 − 0.038 = about 1.63 kg.

So 100 of these bolts weigh about 163 kg without nuts.

L Bolt Weight Example: M24, 750 mm with 150 mm Leg

Steel, 750 mm overall, 150 mm leg, inside bend radius 48 mm (2d), 150 mm of thread.

1. Bend arc = 1.5708 x (48 + 12) = 94.2 mm.
2. Straight length = 750 + 150 − 2 x (48 + 24) + 94.2 = 850.2 mm.
3. Plain bar weight = 0.8502 m x 3.551 kg per metre = 3.019 kg.
4. Thread allowance: 150 mm of M24 thread = 1.5 x 55.3 g = 0.083 kg.
5. Bolt weight = 3.019 − 0.083 = about 2.94 kg.

With a 24 mm (1d) inside radius, the bar is 10 mm longer and the bolt about 0.04 kg heavier.

Adding Nuts and Washers

The examples are for the bolt alone. Our hex bolt weight chart lists ISO 4032 hex nut weights from M6 to M24, up to about 73 g in M20 and 125 g in M24. A DIN 125 plain washer weighs about 17 g in M20 and 32 g in M24.

• M20 J bolt with 2 nuts and 1 washer: 1.63 + 0.15 + 0.02 = about 1.8 kg.
• M24 L bolt with 2 nuts and 1 washer: 2.94 + 0.25 + 0.03 = about 3.2 kg.

Square plate washers are much heavier. Length x width x thickness in mm x 7.85 / 1,000,000 gives their weight in kg, less the hole.

J Bolts and L Bolts from JMIKS Fasteners

JMIKS Fasteners supplies J bolts and L bolts to your drawing length, from M6 to M36 and 1/4″ to 1-1/4″ BSW. Grades are SS 304, SS 316 and SS 202, mild steel 4.6 and 5.6 and high tensile 8.8 and 10.9. Mild steel and high tensile bolts come self colour, zinc plated or hot dip galvanized. Our bolt grade chart explains the grades. For types and setting, read our foundation bolts guide. To weigh a full list of bolts, nuts and washers, use our fastener weight calculator.

Foundation Bolt Weight FAQs

What is the weight of an M20 J bolt?

It depends on the length. M20 bar weighs 2.466 kg per metre. An M20 J bolt 600 mm long, with a hook 100 mm wide and 100 mm of thread, uses about 676 mm of bar and weighs about 1.63 kg without nuts.

How do I calculate foundation bolt weight in kg?

Multiply the straight length of bar in metres, including the bend, by the kg per metre in the chart. Take off the thread allowance, then multiply by the quantity for the weight of an order.

What is the weight of a 20 mm steel rod per metre?

About 2.47 kg. For any round steel bar, kg per metre is about d x d / 162, with d in mm: 400 / 162 = 2.47.

Does the grade change the weight of a foundation bolt?

No. Grade 4.6, 5.6, 8.8 and 10.9 bolts of the same size weigh the same. SS 304 and SS 316 add about 1 to 2 %, and hot dip galvanizing about 0.5 to 1.5 % for a 50 micron coat, more for thicker coats.

Why does a weighed foundation bolt differ from the calculated weight?

Bar is rolled within a small diameter tolerance, bend radii vary and some hooks have a straight tail. Nuts, washers and coating add weight too. A difference of a few percent is normal.

Get a Quote for J Bolts and L Bolts

JMIKS Fasteners is a fastener wholesaler and supplier in Nava Odhav, Ahmedabad. Send the size, overall length, hook or leg length, thread length, grade, finish and quantity on WhatsApp (+91 90333 11425) or through the enquiry form, or get our catalogue from the catalogue page. We reply within one working day.