Force Converter – Newtons, Pound-force and Kilogram-force

Force units and their definitions

Force is mass times acceleration. The SI unit is the newton (N): the force that accelerates one kilogram by one metre per second squared. The converter uses these definitions:

• 1 kilonewton (kN) = 1,000 N
• 1 kilogram-force (kgf) = 9.80665 N, the weight of one kilogram under standard gravity
• 1 pound-force (lbf) = 4.4482216 N, the weight of one pound under standard gravity
• 1 dyne (dyn) = 0.00001 N, the force unit of the older CGS system

Mass versus force

A kilogram is a unit of mass, while a kilogram-force is the force that mass exerts on Earth. Under standard gravity, a 1 kg mass weighs 9.81 N. That is why a load rating of 10 kN is often described as “about one tonne”: 10,000 N ÷ 9.80665 = 1,019.7 kgf. On the Moon, the same kilogram would still have a mass of 1 kg but would weigh only about 1.6 N.

Where force units are used

• Engineering and construction: anchors, bolts, lifting gear and climbing equipment are rated in kilonewtons. A carabiner rated at 24 kN can hold a static load of roughly 2,400 kgf, but ratings include safety margins and must not be treated as everyday working loads.
• US engineering: pound-force appears in thrust ratings, spring forces and structural loads, often written as lbf or simply lb.
• Physics: the newton is used in calculations of work (newton-metre), pressure (newton per square metre) and momentum.

Quick conversions

One newton is about 0.225 lbf or 0.102 kgf. One pound-force is about 4.45 N, and one kilogram-force is about 9.81 N. To estimate kgf from newtons, divide by 10; the error is around 2%. This is handy when a tow bar, shelf bracket or wall anchor is rated in kN and you want to know roughly how many kilograms it can hold.

Sources

Conversion factors follow the SI definitions in the BIPM SI Brochure and the exact factors for US customary and imperial units in NIST Special Publication 811.