How do you calculate the weight of a bolt?

Bolt weight is calculated by modeling the bolt as geometric parts (head or eye ring + shank + bend if applicable), computing the volume of each part, applying a thread reduction factor (0.90 for partial thread, 0.85 for full thread), and multiplying by the material density. Weight = Volume × Density. Standard head dimensions are taken from ISO 4014 / IS 1363 tables.

What is the formula for bolt weight calculation?

For a standard hex bolt: Weight = [0.866 × W² × H + π/4 × D² × L × 0.90] × ρ × Q, where W = width across flats, H = head height, D = nominal diameter, L = length, ρ = material density, Q = quantity. The factor 0.866 × W² is the area of a regular hexagon. The thread reduction factor 0.90 accounts for the difference between nominal and thread root diameter.

How much does an M16 bolt weigh?

An M16 × 100mm mild steel (MS) hex bolt weighs approximately 0.181 kg (181 grams) per piece. This includes the hexagonal head (24mm across flats, 10mm high) and a 100mm shank with 0.90 thread reduction. The exact weight varies slightly with bolt length, head dimensions, and material density.

How much does an M20 bolt weigh in kg?

An M20 × 100mm mild steel (MS) hex bolt weighs approximately 0.298 kg per piece. The head is 30mm across flats × 12.5mm high and the shank uses a 0.90 thread reduction factor. For a longer M20 × 150mm MS bolt, the weight is about 0.409 kg. Stainless steel (SS 304, 8,000 kg/m³) bolts are about 2% heavier than MS for the same dimensions.

What is the density of mild steel for bolt weight calculation?

Mild steel (MS) has a density of 7,850 kg/m³ (0.284 lb/in³). High tensile steel (HT 8.8) is 7,860 kg/m³. Stainless steel 304 and 316 are 8,000 kg/m³. Brass is 8,500 kg/m³ and copper is 8,940 kg/m³. Titanium is the lightest common bolt material at 4,510 kg/m³.

How do you calculate anchor bolt weight?

Anchor bolt weight = [π/4 × D² × L × 0.90 + π/4 × D² × C × 0.85] × ρ × Q, where C is the bend length (L or J portion). The straight shank uses a 0.90 thread reduction, while the bend portion uses 0.85 (full thread). Enter the diameter, straight length, and bend length in the calculator — switch bolt type to 'Anchor Bolt' to see the bend length field.

What is the weight of a hex bolt vs a stud bolt?

A stud bolt (fully threaded rod, no head) of the same diameter and length is lighter than a hex bolt because it has no head. For example, an M16 × 100mm MS hex bolt weighs ~0.181 kg, while an M16 × 100mm MS stud bolt weighs ~0.134 kg — about 26% lighter. The stud also uses a higher thread reduction (0.85 vs 0.90) since it is fully threaded.

How does thread type affect bolt weight?

Threads reduce the effective cross-section of the bolt shank. The calculator applies a 0.90 reduction factor for partially threaded bolts (standard hex, carriage, anchor) and 0.85 for fully threaded bolts (stud). These are conservative engineering estimates — the actual reduction depends on thread pitch, class, and whether threads are cut or rolled.

Can I calculate bolt weight in pounds?

Yes. Toggle the unit system to Imperial (in) and the calculator switches to inches and pounds. Enter diameter and length in inches, and weight displays in pounds. The conversion is exact: 1 kg = 2.20462 lb. Both metric and imperial values are always shown in the weight breakdown section.

Bolt Weight Calculator

Units

Bolt Type

Hexagonal Head Bolt (ISO 4014)

Material

Diameter (mm)

Length (mm)

Quantity

Cost estimate

Price per kg. Total cost = total weight × price per kg.

Hex Bolt · Mild Steel (MS)

Ø16 mm · L 100 mm

Weight per bolt

0.181kg

0.399 lb

Weight Breakdown

Per-piece weight, volume & material details

Weight per piece

0.181kg

0.399 lb

Total weight

0.18kg

Total volume per piece

23.08cm³

1.41 in³

Head volume

4.99 cm³

Shank volume

18.1 cm³

after thread reduction

Nominal diameter

16 mm

Length

100 mm

Material density

7850 kg/m³

Formula Used

The exact formula applied for hex bolt weight

Hex Bolt

Weight = [Head Vol + π/4×D²×L×0.90] × ρ × Q

D = diameter · L = length · ρ = density · Q = quantity · Head Vol = 0.866×W²×H (hex)

Density (ρ) = 7850 kg/m³ (Mild Steel (MS)) · Thread reduction factor = 0.90 (partial thread)

What Is a Bolt Weight Calculator?

Calculate hex, stud, anchor, and eye bolt weight in kg or lb from dimensions and material

A Bolt Weight Calculator is an engineering tool that computes the theoretical weight of bolts from their geometric dimensions and material density. It models the bolt as separate geometric parts — head (hexagonal or disc), eye ring (annular), shank (cylinder with thread reduction), and bend (anchor bolts) — giving precise weight estimates used by structural engineers, procurement teams, steel fabricators, and construction professionals for material ordering, shipping estimation, and load calculations.

bolt types

Hex, Heavy Hex, Carriage, Stud, Anchor, Eye

materials

MS, HT, SS 304/316, EN8, Brass, Copper, Titanium

unit systems

Metric (mm/kg) & Imperial (in/lb)

Bolts are fundamental fasteners in every construction and engineering project — from building frames and bridges to machinery and pipe flanges. Their weight matters because bolts are bought, shipped, and structurally loaded by weight. A standard M16 hex bolt weighs about 0.18 kg, but that changes significantly with bolt type, diameter, length, and material. This calculator covers six bolt types across nine materials, with standard head dimension lookup per ISO 4014 and IS 1363, plus optional cost estimation in 11 currencies.

How to Calculate Bolt Weight

A three-step process from bolt type and dimensions to weight

Select Bolt Type & Material

Choose from 6 bolt types — Hex, Heavy Hex, Carriage, Stud, Anchor, and Eye. Each has a distinct geometry affecting weight. Then pick from 9 materials with built-in densities: Mild Steel (7,850), HT 8.8 (7,860), SS 304/316 (8,000), EN8/EN19 (7,850), Brass (8,500), Copper (8,940), and Titanium (4,510 kg/m³).

Enter Bolt Dimensions

Input the nominal diameter and bolt length in mm or inches. For anchor bolts, also provide the bend (hook) length. For eye bolts, specify the lifting eye outer diameter, inner diameter, and ring thickness. Toggle between metric and imperial — the calculator handles all conversions.

Get Instant Weight Results

See weight per bolt and total batch weight. The calculator shows volume breakdown by part (head, shank, bend, eye ring) with thread reduction applied. Optional cost estimation multiplies total weight by your price per kg in 11 currencies.

Core Formulas by Bolt Type

Hex / Heavy Hex: W = [0.866×W²×H + π/4×D²×L×0.90] × ρ × Q

Carriage: W = [π/4×Dh²×Hh + π/4×D²×L×0.90] × ρ × Q

Stud: W = [π/4×D²×L×0.85] × ρ × Q

Anchor: W = [π/4×D²×L×0.90 + π/4×D²×C×0.85] × ρ × Q

Eye: W = [π/4×(EOD²−EID²)×ET + π/4×D²×L×0.90] × ρ × Q

Where D = nominal diameter, L = shank length, W = width across flats (hex head), H = head height, C = bend length, EOD/EID/ET = eye ring dimensions, ρ = material density, Q = quantity. Thread reduction: 0.90 partial thread, 0.85 full thread (stud).

Worked Example: M16 × 100mm Hex Bolt — Mild Steel

For a standard MS hex bolt (ρ = 7,850 kg/m³):

Head = 0.866 × 24² × 10 = 4,988 mm³
Shank = π/4 × 16² × 100 × 0.90 = 18,096 mm³
Net volume = 4,988 + 18,096 = 23,084 mm³ = 23.08 cm³
Weight per bolt = 23.08 × 7.85 ÷ 1000 = 0.181 kg
Batch of 100 = 0.181 × 100 = 18.1 kg

Bolt Weight Examples at a Glance

Quick reference for commonly used bolt sizes, types, and materials

M16 × 100mm Hex Bolt — MS

0.181 kg

0.399 lb per bolt

Ø16 mm · L 100 mm · Head 24×10 mm

Mild Steel (7,850 kg/m³) · 0.90 thread reduction

M20 × 100mm Hex Bolt — SS 304

0.304 kg

0.670 lb — 2% heavier than MS

Ø20 mm · L 100 mm · Head 30×12.5 mm

Stainless Steel 304 (8,000 kg/m³) · 0.90 thread reduction

M16 × 100mm Stud Bolt — MS

0.134 kg

0.296 lb — 26% lighter than hex

Ø16 mm · L 100 mm · No head

Mild Steel (7,850 kg/m³) · 0.85 full thread reduction

M20 × 300mm Anchor Bolt — HT

0.877 kg

1.933 lb with L-bend

Ø20 mm · L 300 mm · Bend 100 mm

High Tensile (7,860 kg/m³) · bend + shank

Material Density Reference

Standard densities used in bolt weight calculations

Material	kg/m³	lb/in³
Mild Steel (MS)	7,850	0.284
High Tensile (HT 8.8)	7,860	0.284
EN8 Carbon Steel	7,850	0.284
EN19 Alloy Steel	7,850	0.284
Stainless Steel 304	8,000	0.289
Stainless Steel 316	8,000	0.289
Brass	8,500	0.307
Copper	8,940	0.323
Titanium Grade 2	4,510	0.163

Densities shown are typical reference values. Actual density may vary slightly by grade and manufacturing process. Carbon steels (MS, HT, EN8, EN19) share ~7,850 kg/m³, while Stainless 304 and 316 share 8,000 kg/m³. Titanium is 43% lighter than mild steel at 4,510 kg/m³.

Bolt Types Reference

How each bolt type affects the weight calculation

Hex Bolt

Standard hexagonal head per ISO 4014 / IS 1363. Most common fastener for structural and mechanical applications. Partial thread with smooth shank portion. Head volume computed as a regular hexagonal prism.

Heavy Hex Bolt

Larger hex head than standard, per IS 3757. Used in high-strength structural connections, pressure vessels, and flanged joints. Wider bearing surface distributes load across a larger area.

Carriage Bolt

Domed round head with square neck under-head, per DIN 603. Used in wood connections, furniture assembly, and where a smooth finished appearance is required on the exposed side.

Stud Bolt

Fully threaded rod with no head. Used with two nuts for flanged pipe connections or as tie rods. Full thread means 0.85 reduction factor. Lighter than hex bolts of same diameter and length.

Anchor Bolt

L-shaped or J-shaped bolt cast into concrete foundations. The bend provides mechanical anchorage. Common in column base plates, equipment mounting, and heavy structural foundations. Bend calculated as extra shank segment.

Eye Bolt

Looped lifting eye per DIN 580. Eye ring volume = annular ring (π/4×(OD²−ID²)×thickness). Used for rigging, lifting, and tie-down points. Eye dimensions are configurable for non-standard rings.

Tips for Accurate Bolt Weight Calculation

Practical advice for procurement, structural design, and fabrication

Include the head in your weight estimate

For standard hex bolts, the hexagonal head contributes 15–25% of total weight. Stud bolts (no head) of the same diameter and length weigh about 26% less. Always select the correct bolt type.

Use the right thread reduction factor

Partially threaded bolts use 0.90 reduction, fully threaded (studs) use 0.85. This accounts for thread root diameter being ~10% less than nominal. For critical applications, verify against actual thread specifications.

Verify material density for procurement

Copper bolts (8,940 kg/m³) are 14% heavier than mild steel, while Titanium (4,510 kg/m³) is 43% lighter. Selecting the wrong material can cause significant weight estimation errors in shipping and structural calculations.

Count anchor bolt bends separately

The L or J bend on anchor bolts uses full thread reduction (0.85) and is calculated as an additional shank segment. A 100mm bend on an M20 bolt adds about 0.22 kg. Don't skip the bend length for foundation bolts.

Common Mistakes When Calculating Bolt Weight

Avoid these frequent errors that lead to wrong weight estimates

Using bolt length instead of shank length

Standard hex bolt length is measured from under the head to the tip. The head height is calculated separately. For fully threaded bolts, the entire length is threaded — use the stud bolt type.

Ignoring thread reduction entirely

Without thread reduction, weight is overestimated by 10–18%. A fully threaded M16 stud gains ~0.024 kg if calculated as a plain cylinder. The calculator applies this automatically, but manual calculations often miss it.

Mixing diameter conventions across standards

ISO metric bolts use nominal diameter in mm (M16 = 16mm). Imperial bolts use fractional inches. An M16 bolt is NOT interchangeable with a 5/8" bolt (15.875mm). Always use the correct unit system.

Assuming all 'stainless steel' has the same density

SS 304 and SS 316 share 8,000 kg/m³ density but have different corrosion resistance and cost. Austenitic, ferritic, and duplex grades can vary by ±5%. Check the specific grade datasheet for critical jobs.

Frequently Asked Questions

Common questions and detailed answers

IS 1363 is the Indian Standard for hexagon head bolts, equivalent to ISO 4014. It specifies the dimensions of hex head bolts including width across flats, head height, thread length, and nominal diameters from M3 to M64, with extrapolated head dimensions for larger sizes. The calculator uses IS 1363 / ISO 4014 head dimension tables for accurate weight estimation of hex and heavy hex bolts within the standard range.

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Last updated May 18, 2026