Poundals to kilogram-force: absolute units against gravitational ones
A conversion that imports gravity
The poundal belongs to a family of units that never mention gravity. The kilogram-force belongs to the opposite family: one kilogram-force is the pull on a one-kilogram mass in standard gravity, 9.80665 metres per second squared. Converting between the families means importing a value for gravity into a scheme explicitly designed to avoid one. One poundal comes to 0.0140981 kilogram-force, and one kilogram-force is 70.9316 poundals.
Two philosophies, one factor
A gravitational unit is defined by the weight of a standard mass, which makes it intuitive to weigh with and awkward to calculate with, because a hidden 9.80665 sits inside it. An absolute unit is defined by mass and acceleration alone, which keeps the equations clean and the everyday numbers unfamiliar. The factor between the two is not a property of either unit; it is the price of crossing from one convention to the other.
Poundals to kilogram-force compared
Comparable magnitudes in both units, useful when an older specification states a load in kilogram-force and the working calculation is in absolute units.
| Poundal (pdl) | Kilogram-force (kgf) |
|---|---|
| 1 | 0.0140980818502 |
| 10 | 0.140980818502 |
| 25 | 0.352452046254 |
| 50 | 0.704904092509 |
| 100 | 1.40980818502 |
| 1000 | 14.0980818502 |
Why absolute units won the argument
Physicists of the late nineteenth century objected to gravitational units on principle: a unit whose value depends on the local strength of gravity is not a constant, and standards bodies had to fix g artificially to make it behave like one. Absolute units needed no such patch. The objection was sound and eventually decisive, which is why the SI system takes the newton as its coherent unit — even though the kilogram-force is still what many people picture when they imagine a kilogram of force.
Small numbers, easy to misplace
Both units are small, so the ratio is easy to apply backwards. A poundal is about a seventh of a newton and a kilogram-force is nearly ten newtons, which puts roughly seventy-one poundals in one kilogram-force. If a result comes out as a fraction when you expected hundreds, check which way the ratio was applied.
Frequently asked questions
What separates an absolute unit from a gravitational one?
An absolute unit is fixed by mass and acceleration alone, so it holds its value everywhere. A gravitational unit is fixed by the weight of a standard mass, so it only means something once a value for gravity has been agreed. The newton and the poundal are absolute; the kilogram-force and pound-force are gravitational.
Who objected to gravitational units, and why?
Physicists and metrologists around the turn of the twentieth century, who argued that a unit tied to the local pull of the Earth is not a constant and has to be propped up by a defined value of g. Their preference for absolute units shaped the SI system that followed.
Is the kilogram-force still recognised today?
It survives in engineering practice and in some national standards, and the symbol kgf is widely understood, but it is not part of the International System of Units. Modern documents convert to newtons, so a kilogram-force figure usually appears in older specifications or in fields that never switched.
How do the two units compare in everyday terms?
A kilogram-force is about the weight of a litre of water and equals 9.80665 newtons. A poundal is far smaller, roughly the force that accelerates a pound by a foot per second squared, so about seventy-one of them are needed to balance a single kilogram-force.
Why is a gravity value needed for this conversion at all?
Because one of the two units is built from gravity and the other is not. The poundal needs only the pound and the foot, while the kilogram-force needs the kilogram plus standard gravity. Any bridge between them has to supply that missing constant, and 0.0140981 is where it enters.