# Quick question on weight/mass [duplicate]

(In the US, just to clarify)So, from a physics perspective weight and mass are different, but when people are talking about weight in everyday(non-physics) situations ("how much do you weigh" etc.), are they actually talking about mass and it's just common to refer to it as 'weight'?

Expanding on that, when you step on a scale, i've read it displays your mass(after conversion from weight as it's displaying the "results"). Seeing as pounds is a measurement of weight, why will it use pounds as a unit of mass?

Maybe i'm getting things completely confused, any help is appreciated.

• Possible duplicates: physics.stackexchange.com/q/43195/2451 and links therein. Apr 11, 2016 at 17:55
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– user10851
Apr 12, 2016 at 3:03

your mass is independent of gravity (ignoring relativity). in space (or on the moon) your scale would not show what it shows on Earth, so it can't be measuring your mass. a scale measures weight, but sometimes converts to mass via $$Weight = 9.8 N/kg * Mass$$ (near surface of Earth)

• Sorry, i meant after conversion , when it's displaying your "results" as mass. I'll clarify in the main post Apr 11, 2016 at 18:40

When you are looking at the car speedometer you are actually measuring AN ANGLE between the zero and dial hand. Nevertheless, you read SPEED units.

This is because scale is CALIBRATED in units of speed.

Similarly, when you are looking at mercury thermometer, you are actually measuring the DISTANCE. Nevertheless, you read TEMPERATURE units.

This is because device is CALIBRATED in units of temperature.

This is the common case in metrology: you are transforming physical quantities one to another and finally get easy observable and CALIBRATE it.