What is mass?
Mass is typically defined as the amount of matter within an object. It is most commonly measured as inertial mass, involving an object's resistance to acceleration given some net force. Matter, however, is somewhat loosely defined in science, and cannot be precisely measured. In classical physics, matter is any substance that has mass and volume.
The amount of mass that an object has is often correlated with its size, but objects with larger volumes do not always have more mass. An inflated balloon, for example, would have significantly less mass than a golf ball made of silver. While many different units are used to describe mass throughout the world, the standard unit of mass under the International System of Units (SI) is the kilogram (kg).
There exist other common definitions of mass including active gravitational mass and passive gravitational mass. Active gravitational mass is the measure of how much gravitational force an object exerts, while passive gravitational mass is the measure of the gravitational force exerted on an object within a known gravitational field. While these are conceptually distinct, there have not been conclusive, unambiguous experiments that have demonstrated significant differences between gravitational and inertial mass.
Mass vs. Weight
The words mass and weight are frequently used interchangeably, but even though mass is often expressed by measuring the weight of an object using a spring scale, they are not equivalent. The mass of an object remains constant regardless of where the object is and is, therefore, an intrinsic property of an object. Weight, on the other hand, changes based on gravity, as it is a measure of an object's resistance to its natural state of freefall.
The force of gravity on the moon, for example, is approximately one-sixth that on earth, due to its smaller mass. This means that a person with a mass of 70 kg on earth would weigh approximately one-sixth of their weight on earth while on the moon. Their mass, however, would still be 70 kg on the moon. This is in accordance with the equation:
Where F is force, G is the gravitational constant, m₁ and m₂ are the mass of the moon and the object it is acting upon, and r is the moon's radius.
In the metric system, weight is measured in Newtons following the equation W = mg, where W is weight, m is mass, and g is the acceleration due to the gravitational field. On earth, this value is approximately 9.8 m/s². It is important to note that regardless of how strong a gravitational field may be, an object that is in free fall is weightless. In cases where objects undergo acceleration through other forces (such as a centrifuge), weight is determined by multiplying the object's mass by the total acceleration away from free fall (known as proper acceleration).
How to Use This Calculator
While mass is defined by F = ma, in situations where density and volume of the object are known, mass is also commonly calculated using the equation below. This is the logic applied by our calculator.
- Enter the density: Input the numeric value of the density and choose the correct unit of density (e.g. kg/m³ or lb/ft³) from the dropdown.
- Enter the volume: Input the volume of your object and ensure the corresponding volume unit (like cubic meters or liters) is accurately selected.
- Calculate: The calculator instantly standardizes these units and computes the total mass of the object, offering a clean table of output measurements from metric tons down to atomic mass units.
The Formula
By rearranging the standard density equation (density = mass / volume), you can quickly solve for mass if you know the object's total volume and intrinsic density:
m = Mass
ρ (rho) = Density
V = Volume
The SI unit for density is kilogram per cubic meter, or kg/m³, while volume is expressed in m³, and mass in kg.
Frequently Asked Questions
Mass is the amount of matter in an object and remains constant regardless of location. Weight is the gravitational force acting on that mass. For example, your mass is the same on Earth and the Moon, but you weigh much less on the Moon because its gravity is weaker.
Under the International System of Units (SI), the base unit of mass is the kilogram (kg). Other common metric units include grams (g) and milligrams (mg). Imperial equivalents heavily used in the US include the pound (lb) and ounce (oz).
You can calculate mass by multiplying the object's density by its volume. The formula is m = ρ × V. Always ensure that the units for density and volume are compatible before multiplying them, or use a tool like this calculator which converts the units for you.
In classical physics, all matter must have both mass and volume. Therefore, physical objects cannot have zero mass. However, in particle physics, certain fundamental particles like photons (particles of light) are considered to be "massless".
No. Mass depends on both volume and density. A very large object made of a low-density material (like a giant balloon filled with helium) will have less mass than a much smaller object made of a high-density material (like a solid lead ball).