What Is a Newton? The SI Unit of Force

One newton is the force that gives a mass of one kilogram an acceleration of one meter per second squared: 1 N = 1 kg·m/s². It is a derived unit of the International System of Units (SI).

The unit is named after Isaac Newton. His second law of motion, F = m × a, is exactly the relationship the definition uses.

Under standard gravity (9.80665 m/s²), a mass of about 101.97 grams weighs one newton. That is roughly the weight of a small apple.

A person with a mass of 70 kg weighs about 686.5 N under standard gravity.

• 1 N ≈ 0.2248089431 lbf
• 1 N ≈ 0.1019716213 kgf
• 1 N = 100000 dyn (exact)
• 1 kN = 1000 N (exact)

Newtons appear wherever force is measured in SI units: physics, mechanical and civil engineering, load ratings of hardware, and material testing. Stress and pressure build on it too: one pascal is one newton per square meter, and one megapascal equals one newton per square millimeter.

• A load of 500 N is 112.404 lbf: divide by 4.4482216152605.
• A force of 25 lbf is 111.206 N: multiply by 4.4482216152605.
• A rating of 2.5 kN is 2500 N: multiply by 1000.

These factors are fixed by definition, so the results do not depend on where on Earth you are. Only conversions that involve kilogram-force assume standard gravity.

Many SI units are built from the newton. Work and energy: one joule is one newton acting over one meter (1 J = 1 N·m). Pressure and stress: one pascal is one newton per square meter (1 Pa = 1 N/m²). Torque: the newton meter (N·m), which has the same dimensions as the joule but is never written in joules.

Because of this, a pressure of 1 MPa is the same as 1 N/mm², a convenient form for material strength. 145.038 psi is 1 MPa.

• Writing the unit with a capital letter. The unit name is "newton" in lowercase; only the symbol N is a capital letter, because the unit is named after a person.
• Treating a reading in kilograms as a force. A scale shows mass in kg; the force on the scale is that mass times the acceleration of gravity, measured in newtons.
• Mixing N and kN in one calculation. Convert everything to the same unit first, then calculate.