In fields such as engineering, manufacturing, and even everyday home improvement projects, it is important to understand different units of measurement.
In this article we are primarily aimed at readers in the UK. If you’re in this part of the world, you may need to be particularly adept at juggling between metric (e.g. kilograms) and imperial (e.g. pounds) systems.
However, when it comes to the specific units we mentioned at the top of this article, confusion can often arise as to whether they measure mass or force/weight.
So before we jump straight into the topic of converting between these units, we first wanted to provide some clarity on these important topics.
Understand the key differences
When it comes to the basic physical quantities involved in these conversions, consider the following:
- Mass is a measure of the amount of matter in an object. The mass, measured in kilograms or pounds, remains constant regardless of location.
- Force/weight, on the other hand, is a measure of the attraction of gravity on this mass. It is measured in Newtons and can vary depending on the gravitational field.
So if you need to convert mass (kg, lb) directly to force (N) due to a specific application or circumstance, you need to take gravity into account.
Now let’s turn back to the specific units of measurement:
- Kilograms (kg) are a unit of mass in the metric system. It is what weighs something in a vacuum or on a scale.
- Pound (lb) is primarily a unit of mass in the imperial system. However, there can be some confusion here as in everyday usage in the UK what is often referred to as “weight” is the force caused by gravity.
- Newton (N) is a unit of force in the International System of Units (SI). Since weight is a force, if you want to convert mass to weight in newtons, you must multiply by gravity (approximately 9.81 meters per second squared, or m/s2 on Earth). For example, a mass of 1 kg weighs approximately 9.81 N).
Mixing up these units risks making errors in load capacity calculations or shipping specifications. It is therefore important to always clarify whether in a particular situation it is mass (for scales) or force (for tension or pressure).
Conversion between kilograms and pounds (mass)
So let’s move on to the conversion formulas themselves. Because kilograms and pounds are units of mass, converting between them is easy using a fixed ratio:
- 1 kilogram (kg) is approximately equal to 2.20462 pounds (lb). So to convert from kg to lb, multiply the mass in kg by 2.20462.
- 1 pound (lb) is approximately equal to 0.453592 kilograms (kg). So to convert from lb to kg, multiply the mass in lb by 0.453592.
Convert mass (kg, lb) to force (Newton).
To determine the weight of an object in Newtons, you can use the formula: Force (N) = Mass (kg) x Acceleration due to gravity (g). To be relatively precise, on Earth the standard acceleration due to gravity (g) is approximately 9.80665 m/s2.
So to convert:
- When converting kg to N (on Earth), you need to multiply the mass in kg by 9.80665.
- To convert lb to N (on Earth), you must first convert pounds to kilograms and then multiply by 9.80665.
One more thing about converting between units of measurement…
Finally, don’t forget that you don’t always have to do your calculations “by hand” when converting weight.
For example, you can point your browser to the website of electrical components supplier RS and perform quick calculations using the weight and mass conversion calculator.
Because if you rely solely on manual calculations, especially if you have to make many such conversions, the time required can quickly add up. Additionally, rounding errors can easily creep in, potentially having a negative impact on the rest of your project or task.
So it may well be worth having one or two reputable weight conversion tools saved in your bookmarks for the next time you might need them to ensure fast, accurate and versatile calculations.
