Convert Force from Pound-forces to Kilogram-forces (lbf to kgf)

Pound-force to Kilogram-force Conversion Formula

Example

Let's convert 5 Pound-force (lbf) to Kilogram-force (kgf).

Using the formula:

Therefore, 5 Pound-force (lbf) is equal to 2.2678800856531049251 Kilogram-force (kgf).

How many pound-forces are in one kilogram-force? One Kilogram-force (kgf) contains 2.2047021055613256539 Pound-forces (lbf) — the inverse of the factor above. Multiplying by 0.45357601713062098501 takes you from pound-forces to kilogram-forces; multiplying by 2.2047021055613256539 brings you back.

Put in words: one pound-force equals 0.45357601713062098501 kilogram-forces, so the pound-force is the smaller unit of this pair. Converting between them never changes the amount of force being measured — only the size of the unit you count it in.

What Is a Pound-force (lbf)?

A pound-force (lbf) is the force that gravity exerts on a mass of one pound at the Earth's surface. It is the standard unit of force in the US customary and imperial systems.

• 1 lbf = 4.44822 N (exactly, by definition of the standard pound and standard gravity)

Pound-force Versus Pound-mass

This is the single most common source of error in imperial calculations. The pound (lb) is a unit of mass; the pound-force (lbf) is a unit of force. They share a name and are numerically equal only at standard gravity on Earth.

Engineering documents disambiguate them by writing lbm for pound-mass and lbf for pound-force. When a specification says "50 lb" without qualification, check the context: a bolt torque is force, a shipping weight is mass.

Where Pound-force Is Used

• US mechanical engineering — spring rates, actuator and cylinder ratings, clamp loads.
• Aerospace — jet engine thrust is almost always quoted in lbf or klbf (thousands of pound-force), even outside the United States.
• Fastener specifications — proof loads and tensile strengths in US standards.
• Consumer hardware — drawer slides, gas struts and latches sold in the US market.

Everyday Reference Points

• A firm handshake exerts roughly 20 lbf.
• A domestic door closer resists about 10–15 lbf.
• A single CFM56 jet engine produces around 27,000 lbf of thrust.

Converting Pound-force

What Is a Kilogram-force (kgf)?

A kilogram-force (kgf), also called a kilopond (kp), is the force exerted by gravity on a mass of one kilogram at standard gravity.

• 1 kgf = 9.807 N

A Metric Unit That Behaves Like an Imperial One

The kilogram-force is a gravitational metric unit: it takes the convenience of the imperial system — where the number on the scale and the number in the force calculation match — and applies it to metric mass. If a load is 250 kg, its weight is simply 250 kgf.

That convenience is also why the unit was deprecated. It bakes the Earth's gravity into the definition, so any calculation using it silently assumes you are standing on this planet at sea level. The SI system replaced it with the newton, and modern standards discourage kgf in new work.

Where You Still Meet It

Deprecated does not mean gone. Kilogram-force still appears in:

• Older machinery and technical drawings, particularly European and Japanese equipment made before the 1990s.
• Tyre and pressure gauges in some markets, where kgf/cm² is used instead of bar.
• Torque wrenches graduated in kgf·m or kgf·cm.
• Medical and fitness equipment — grip strength dynamometers commonly read in kgf.

If you are reading an old service manual, expect kgf. If you are writing a new specification, use newtons.

Converting Kilogram-force

Pound-force to Kilogram-force Conversion Table

Here are some quick reference conversions from Pound-force (lbf) to Kilogram-force (kgf):