# Does a scale *display* weight or mass?

• AmagicalFishy
In summary, bathroom scales measure weight, which is a force, by calculating the displacement of a spring. The displayed numbers represent weight divided by a factor to display mass. However, this factor is calibrated for the Earth's surface, so using the scale on the moon would give incorrect values. Some scales may display the unit of measurement, but most assume a standard g level of 9.80665 (m/s)/s and display mass.
AmagicalFishy
I know that scales measure weight (a force) via displacement of a spring. I also know the difference between a force and a mass. I know that, on the moon, the numbers on a scale might be different (depending on the answer to this question). I've read through the few threads on this matter here, and there isn't a clear answer to my question:

What are the numbers that a bathroom scale actually displays? Are the numbers displayed a force, or does the scale implicitly assume it is on Earth, account for this—and thus display a mass?

There's been quite a few threads on this subject over the years
have a look down at the bottom of your thread page and you will see some of the similarly titled threads
have a look through and see if they answer your questions ... if there is still anything unclear

cheers
Dave

The scale measures force, that is weight. But instead of displaying force or weight, the numbers you see are weight divided by a factor, the downwards accelaration on the Earth's surface, so as to display mass.

If you used such a scale on the moon, the values would be incorrect, although you could easily make the correction by simply multiplying the correct factor.

AmagicalFishy said:
What are the numbers that a bathroom scale actually displays?
Is there no unit displayed or written on your scale?

AmagicalFishy said:
I know that scales measure weight (a force) via displacement of a spring. I also know the difference between a force and a mass. I know that, on the moon, the numbers on a scale might be different (depending on the answer to this question). I've read through the few threads on this matter here, and there isn't a clear answer to my question:

What are the numbers that a bathroom scale actually displays? Are the numbers displayed a force, or does the scale implicitly assume it is on Earth, account for this—and thus display a mass?

Most scales are calibrated for one value of g. So if you put a known mass on a scale it will read slightly differently at different places on the Earth (eg near a mountain where g is very slightly higher or on the moon where it's lower). That demonstrates they are measuring and displaying weight not mass.

If you wanted them to measure weight but display mass they would have to automatically correct for variations in g.

Edit; You could make one that measured and displayed mass - for example by counting atoms or perhaps by using a horizontal spring and vibrating the mass.

Last edited:
Scales assume a local g level of 9.80665 (m/s)/s, the result is mass (kg) and weight (kgf) provided your at the Earth's surface radius.

## 1. What is the difference between weight and mass?

Weight is a measure of the force exerted on an object due to gravity, while mass is a measure of the amount of matter in an object.

## 2. How does a scale measure weight?

A scale measures weight by using a spring or strain gauge to determine the amount of force exerted on the object being weighed.

## 3. Why is weight displayed in units of force, such as pounds or kilograms?

Weight is displayed in units of force because it is a measurement of the force exerted on an object due to gravity.

## 4. Can a scale also display mass?

No, a scale cannot display mass as it is not capable of directly measuring mass. Mass can be calculated from weight by using the formula W=mg, where W is weight, m is mass, and g is the acceleration due to gravity.

## 5. Is the weight displayed by a scale affected by the location or environment?

Yes, the weight displayed by a scale can be affected by the location or environment due to the variation in the acceleration due to gravity. For example, weight will be slightly different on Earth compared to the moon due to the difference in gravitational pull.

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