Force Converter (N, kgf, lbf, dyn)

Understanding the force converter — concept and principle

Force is a push or pull that changes an object's motion. This converter switches between newtons (N), kilonewtons (kN), kilogram-force (kgf), tonne-force (tf), pound-force (lbf) and dynes (dyn). It is useful when reading load ratings, spring and tension specifications, torque-related data or older engineering documents that use gravitational units.

How it is calculated

The calculator converts the value into newtons and then into the target unit: result = value × (N per source unit) ÷ (N per target unit). The factors are:

• 1 kN = 1,000 N
• 1 kgf = 9.80665 N (exact, by definition)
• 1 tf = 1,000 kgf = 9,806.65 N
• 1 lbf = 4.4482216152605 N (exact, from the pound and standard gravity)
• 1 dyn = 10⁻⁵ N (the CGS unit: 1 g × 1 cm/s²)

The principle

Newton's second law, F = m × a, defines the newton: the force that accelerates 1 kg at 1 m/s². Gravitational units instead use the weight of a standard mass under standard gravity, g₀ = 9.80665 m/s², a value fixed by international agreement in 1901. So 1 kgf is the weight of 1 kg under g₀: 1 kg × 9.80665 m/s² = 9.80665 N. The pound-force follows the same idea with the avoirdupois pound (0.45359237 kg exactly): 0.45359237 × 9.80665 = 4.4482216152605 N. Because both use the same g₀, the ratio kgf : lbf equals the ratio kg : lb.

Worked example

1. Inputs: 1 kgf, convert to newtons.
2. 1 kgf = 1 kg × 9.80665 m/s² = 9.80665 N.
3. In kilonewtons: 9.80665 ÷ 1,000 = 0.00980665 kN.
4. In pound-force: 9.80665 ÷ 4.4482216152605 = 2.204622622 lbf.
5. In dynes: 9.80665 × 100,000 = 980,665 dyn; in tonne-force: 0.001 tf.

How to read the result

A useful rule of thumb is 1 kgf ≈ 10 N, accurate to about 2%. An apple weighs roughly 1 N, an adult of 70 kg weighs about 686 N, and a 1 tonne car presses on the ground with about 9.8 kN. Engineering data in SI should be given in N or kN; kgf values still appear on older drawings, gauges and Asian product labels.

Common mistakes

• Treating kg and kgf as the same unit. Mass in kg does not change with location; weight in N does.
• Using 9.8 or 10 instead of 9.80665 when an exact conversion is needed.
• Confusing tonne-force (1,000 kgf) with US short ton-force (2,000 lbf).
• Mixing force units with torque units such as N·m or kgf·m.

Frequently asked questions

How many newtons is 1 kgf?

Exactly 9.80665 N.

Why do bathroom scales show kg if they measure force?

A scale measures the force your weight puts on it and divides by an assumed gravity to display mass.

How do I convert lbf to N?

Multiply by 4.448221615. For example, 100 lbf ≈ 444.8 N.

Sources: BIPM, The International System of Units (SI Brochure), 9th edition · NIST Special Publication 811 (2008), Appendix B