Bolt Torque and Ultimate Load Table (ISO 898-1)

This page provides engineering data for bolt torque, tensile load and proof load calculations for metric fasteners based on ISO 898-1. It is used for estimating tightening torque and preload in bolted joint design.

Bolt Load, Proof Load and Torque Data

In accordance with BS EN ISO 898-1 : 1999

Important: These torque values are approximate and should only be used as a guide. Actual tightening torque depends on lubrication, surface finish and friction conditions.

The table below provides approximate tensile loads, proof loads and torque values for metric bolts of different strength grades based on ISO 898-1.

Note: Torque-based tightening is highly sensitive to friction variation, which can introduce errors of ±25% or more in preload.

	-	FASTENER SIZE
	-	M6	M8	M10	M12	M14	M16	M20	M22	M24	M30	M36
Pitch	mm	1.0	1.25	1.50	1.75	2.0	2.0	2.5	2.5	3.0	3.5	4.0
Stress Area	mm²	20.1	36.6	58	84.3	115	157	245	303	353	561	817

-	GRADE	-	-	-	-	-	-	-	-	-	-	-
Minimum Tensile Load (kN)	4,6	8,04	14,6	28,2	33,7	46	62,8	98	121	141	224	327
	8,8	16,1	29,2	46,4	67,4	92	125	203	252	293	466	678
	10,9	20,9	38,1	60,3	87,7	120	168	255	315	367	583	850
	12,9	24,5	44,6	70,8	103	140	192	299	370	431	684	997

Proof Loads (kN)	4,6	4,52	8,24	13	19	25,9	35,3	55,1	68,2	79,4	126	184
	8,8	11,6	21,2	33,7	48,9	66,7	91	147	182	212	337	490
	10,9	16,7	30,4	48,1	70	95,5	130	203	212	293	466	678
	12,9	19,5	35,5	56,3	81,8	112	152	238	294	342	544	792

Maximum Torque Nm	4,6	4,6104	11,2064	22,1	38,76	61,642	96,016	187,34	255,068	323,952	642,6	1126,08
	8,8	11,832	28,832	57,29	99,756	158,746	247,52	499,8	680,68	864,96	1718,7	2998,8
	10,9	17,034	41,344	81,77	142,8	227,29	353,6	690,2	792,88	1195,44	2376,6	4149,36
	12,9	19,89	48,28	95,71	166,872	266,56	413,44	809,2	1099,56	1395,36	2774,4	4847,04

Related RoyMech Bolt Load Calculators

Use these calculators for practical bolt load, preload and tightening calculations.

Calculator	Use
Bolted Joint and Fastener Calculators	Main hub for RoyMech bolt and fastener calculation tools.
Bolt Preload Calculator	Estimate preload from tightening torque, bolt diameter and nut factor.
Bolt Tightening Torque Calculator	Calculate tightening torque from a target bolt preload.
Bolt Proof Load Calculator	Calculate proof load from proof stress and tensile stress area.
Bolt Tensile Stress Calculator	Calculate tensile stress in a bolt from axial load.
Bolt Combined Stress Calculator	Check combined tensile and shear stress using the Von Mises method.

Bolt Load Definitions

Stress Area: Effective area used for strength calculations
Proof Load: Maximum load without permanent deformation
Tensile Load: Maximum load before failure
Torque: Tightening moment applied to the bolt

Bolt Torque Calculation

Bolt torque is estimated using:

Torque = K × F_m × d

Where:
K = friction factor (typically 0.2)
F_m = bolt preload (≈ 0.85 × proof load)
d = nominal diameter (m)

Note: Torque-based tightening is highly sensitive to friction variation and can introduce errors of ±25% or more in preload.

Applications of Bolt Load and Torque Data

Bolt tightening and assembly procedures
Structural and mechanical joint design
Preload and clamping force calculations
Maintenance and repair operations
General engineering and construction

Advantages of Using Torque Tables

Quick estimation of tightening torque
Supports safe bolt loading
Reduces risk of under or over tightening
Based on recognised standards
Easy reference for engineers and technicians

Limitations of Torque Tables

Values are approximate only
Friction conditions can vary widely
Does not account for lubrication differences
Accuracy depends on correct preload assumptions
Not suitable for critical high-precision joints

Frequently Asked Questions

How is bolt torque calculated?

Bolt torque is calculated using Torque = K × Fₘ × d, where K is a friction factor, Fₘ is preload and d is bolt diameter.

What is proof load?

Proof load is the maximum load a bolt can sustain without permanent deformation.

What is ultimate tensile load?

Ultimate tensile load is the maximum load a bolt can carry before failure.

Why are torque values approximate?

Torque values depend heavily on friction, lubrication and surface conditions, which vary in practice.

What does bolt grade 8.8 mean?

It indicates tensile strength and yield strength properties according to ISO standards.

Should torque tables be used for critical joints?

No, more accurate methods such as tension measurement or controlled tightening should be used.

Bolt Ultimate Loads, Proof Loads and Torque Values