Force Units

The Newton (N) is the SI unit of force: 1 N = 1 kg·m/s². Other common units include:

Unit	= Newtons	Notes
1 dyn	0.00001	CGS unit (1 g·cm/s²)
1 pdl	0.138255	Poundal (1 lb·ft/s²)
1 N	1	SI unit
1 daN	10	Decanewton ≈ 1 kgf
1 kgf	9.80665	Kilogram-force (= 1 kg × g)
1 lbf	4.44822	Pound-force
1 kN	1000	Kilonewton
1 kip	4448.22	Kilopound (1000 lbf)
1 MN	1000000	Meganewton

Common Equivalences

1 kgf = 9.80665 N (exactly, by definition of standard gravity)

1 lbf = 4.44822 N

1 daN ≈ 1.0197 kgf (often used interchangeably in European practice)

Common Engineering Force Values

From → To	Multiply by	Example
N → lbf	0.22481	100 N = 22.48 lbf
lbf → N	4.44822	100 lbf = 444.8 N
N → kgf	0.10197	100 N = 10.20 kgf
kgf → N	9.80665	100 kgf = 980.7 N
kN → kip	0.22481	10 kN = 2.248 kip
kip → kN	4.44822	1 kip = 4.448 kN

Force in Engineering Applications

• Bolt preload: Typically expressed in kN (e.g., M16 class 8.8 → preload ~50 kN)
• Press fits: Force in kN or tonnes-force
• Spring force: N or lbf, with spring rate in N/mm or lbf/in
• Hydraulic cylinders: F = P × A (pressure × area), typically kN or tons
• Bearing loads: kN (dynamic and static capacity ratings)
• Structural loads: kN for beams, kip for US structural steel
• Lifting/rigging: Rated in tonnes (metric tons-force) or tons (short tons)

Newton’s Second Law

The Newton is defined through F = m × a:

• 1 N = 1 kg × 1 m/s² (force to accelerate 1 kg at 1 m/s²)
• 1 dyn = 1 g × 1 cm/s² (CGS equivalent)
• 1 pdl = 1 lb × 1 ft/s² (imperial absolute unit)
• Weight on Earth: W = m × g where g = 9.80665 m/s²

Quick Mental Estimates

• 1 kgf ≈ 10 N (actually 9.807 N — within 2%)
• 1 lbf ≈ 4.5 N (actually 4.448 N — within 1%)
• 1 kN ≈ 100 kgf ≈ 225 lbf
• 1 tonne-force ≈ 10 kN (actually 9.807 kN)
• 1 kip ≈ 4.5 kN