Mass is the quantity of matter in an object. A heavy object has more matter in it than a light one, so it has greater mass.

The most common unit for mass is the kilogram, which is 1000 grams (g). Students can learn about the 7 SI base measurement units with this comic book-style video.

Definition

The most basic property of matter is its mass. An object’s weight varies with its environment because of the gravitational pull of the Earth on it. A heavy object has more matter in it than a light one, so it has greater mass.

However, the density of the object is a factor as well, and differs between objects with the same mass. In fact, a scale can be calibrated to produce different results depending on whether the mass is measured against a stainless steel standard or an air standard.

The SI unit for measuring mass is the kilogram (kg), which was first characterized in 1795 as one cubic decimeter of water at the melting point of ice. One kilogram is equal to 1000 grams. The atomic mass unit is a more precise way to measure an atom’s or particle’s mass; it is defined as 1/12th the mass of a Carbon-12 atom. This measurement method allows for a more accurate calculation of mass in cases where the physical prototype of a kilogram is not available.

Units

The units of mass are kilograms (kg) and grams in the metric system and pounds or ounces in the US customary and British imperial systems. Weight is a measure of the inertial property of matter and depends on an object’s location, so it can change with its environment.

All measuring systems have basic units of length, mass, capacity (volume), and temperature. These are called the fundamental or base measurement units. They are defined for only these physical quantities. Other measurements are derived from these, such as velocity, which is determined by dividing a distance quantity by a time quantity, like meters per second or micrometers per nanosecond.

The standard unit of mass in the metric system is the kilogram, which is defined as the mass of a specific artifact in Paris known as the International Prototype Kilogram, or kg. This artifact is maintained by the BIPM, and copies of it are distributed to countries that have signed a diplomatic treaty to become members of the metric system.

Conversions

Some physical quantities have multiple units that can be used to describe them. Conversions between these units occur frequently. These conversions can be made using unit ratios and dimensional analysis. For example, converting inches to centimeters involves multiplying the number of inches by the conversion factor of 10 and then dividing by 100.

The most common types of conversions involve mass and weight measurements. While the United States continues to largely use customary units, many other countries have adopted the International System of Units (metric/SI) of measurement. Therefore, it is important for people across the globe to be able to communicate with one another about these measurements. To help with this communication, this page contains many helpful links to conversion tables and other resources. Several of these resources also contain practice problems. This page also includes a handy applet that allows users to convert between metric and US Customary units. Simply enter the starting units in the upper left corner and the desired units in the lower left corner, then click “go”. This applet also allows users to make mass conversions from liters to quarts.

Applications

Mass measurement is crucial to a variety of applications, from food inspection and quality control to drug testing and discovery, carbon dating, isotope ratio determination and forensic toxicology. It is particularly important in proteomics, where accurate masses are critical for protein identification and for delineating cellular networks and pathways in systems biology studies.

During mass photometry, the light scattered by a sample molecule in contact with a measurement surface interferes with the light reflected by that surface and is measured; this interference signal scales linearly with molecular mass. The resulting mass value is then compared with a known estimate of mass to calculate the sample’s gross mass.

Proteomics applications that rely on accurate mass measurements benefit from rapid developments in both MS instrumentation and databases. These include protein identification by matching parent ions or fragment ions with theoretical masses based on the sequences of proteins in genomic databases, as well as the detection of posttranslational modifications.

In food production, accurate weighing is an integral part of the manufacturing process. It ensures that all ingredients are added in the right order and proportion, maintaining product quality.

When weighing with high-precision analytical balances, it is important to tare the container before adding the sample. This reduces the error caused by differences in air currents between the weighing pan and the underlying mass.

Accuracy

Accuracy is the closeness of measurement results to their true value. This includes both trueness (the number of measurement results that fall within a statistical distribution) and precision (repeatability or the spread of measurements over time).

The accuracy of a weighing instrument is primarily determined by its load cell(s). These sensors are made from machined pieces of metal with strain gauges bonded at points on the surface, which bend with the weight of an object, then converts mechanical pressure into a proportional electrical signal for display in the instrument.

Choosing a high-quality load cell is the first step to ensuring accurate weighing. A quality balance is also important, along with calibrating and maintaining it on a regular basis using certified calibration weights. GWP helps eliminate confusion over terms like resolution, division size, readability and accuracy by requiring that all four requirements are met for good measurement practice.

Efficiency

Weighing process efficiency is a vital aspect of any production facility. Inaccurate measurements can result in wasted resources, a loss of profit, and even health risks for consumers. To ensure that weighing processes run smoothly, manufacturers should invest in the right equipment.

Process weighing refers to the integration of scales into production systems that automatically measure and dispense materials according to predetermined criteria. This technology is commonly used in sectors like food and pharmaceuticals to optimize production and reduce waste.

Automated weighing systems can also help speed up onboarding times. Their user-friendly interfaces eliminate the need for complex manual processes, allowing new employees to learn the ropes faster and mitigate the risk of beginner errors. The best weighing systems also feature validation tools that simulate the operating conditions of the system and provide comparisons to expected results. These data are then used to improve the accuracy and reliability of the weighing system. This can greatly reduce the time and effort required to maintain a production line.

Safety

Safe weighing practices are critical in hazardous industrial environments. Any miscalculations in these settings can cause safety hazards, product loss, and tarnished brand reputation.

Weighing equipment used in hazardous locations must be specially designed to mitigate potential hazards. This includes scales certified for use in areas with explosive vapors or dust, such as those used in large bakeries (flour), plastics manufacturing plants (vapors), and chemical plant silos (dust or “flyings”).

These hazardous environments require high-quality, reliable equipment to ensure accurate measurements. Weighing equipment in these environments must also be able to withstand the effects of prolonged exposure to hot and cold temperatures, as well as corrosion from caustic chemicals. Regular inspections and maintenance are necessary to keep these scales in top condition.

Compliance

Weighing is a vital step within the food production process to ensure that ingredients meet recipe specifications. It helps manufacturers meet quality control standards and ensures that every batch looks, tastes, and smells the same as the last. A digital solution makes this entire process more manageable and improves regulatory compliance.

Always use a clean container to receive the weighed substance. The container should never touch the weighing pan of an analytical balance as even the slightest moisture can cause a discrepancy in the mass reading. The container used should also be a suitable size for the capacity of the balance.

It is a good practice to close the balance doors during the weighing process to prevent air currents that may disturb the reading. Additionally, it is important to keep the area where the weighing takes place free of dust and contaminants since this can affect the accuracy of the readings. Lastly, it is important to make sure that the weighing system is properly leveled and zeroed before attempting any weighings.