Mass Calculator — Free Online Mass Unit Converter

How to Use the Mass Calculator

1. Enter the mass value: Type the mass you want to convert into the Mass Value field. The calculator accepts any positive number, including very small values like 0.001 (for milligram-level conversions) and very large values like 1000000 (for tonnage). Decimal values are fully supported for precise measurements from laboratory scales, shipping manifests, or recipe ingredients.
2. Select the source unit: Use the From Unit dropdown to choose the unit of your input value. Eight units are available: kilogram (kg), gram (g), milligram (mg), pound (lb), ounce (oz), US ton (short ton), metric ton (tonne), and stone (st). Select the unit that matches your original measurement or the unit system you are starting from.
3. View all conversions at once: The results panel displays your mass converted to all seven other units simultaneously. This makes it easy to find the specific unit you need without performing multiple separate conversions. The display is organized from largest to smallest units for quick reference.
4. Adjust and compare: Change the input value or source unit at any time to see updated results in real time. This feature is useful for comparing weights in different unit systems, converting recipe ingredients, calculating shipping weights, or checking homework problems across multiple units.

All conversions use the standard international conversion factors defined by the International Bureau of Weights and Measures (BIPM). Results are displayed with up to six decimal places for maximum precision.

Mass Conversion Formulas

Variables Explained

• Kilogram (kg): The SI base unit of mass, defined since 2019 by fixing the value of the Planck constant. One kilogram is approximately the mass of one liter of water at 4 degrees Celsius. Used worldwide in science, commerce, and everyday life outside the United States.
• Gram (g): One thousandth of a kilogram. Commonly used for food packaging, cooking recipes, and smaller item weights. A standard paper clip weighs about 1 gram, and a US nickel weighs 5 grams.
• Milligram (mg): One thousandth of a gram or one millionth of a kilogram. Primarily used in pharmaceuticals for drug dosages and in nutrition labels for vitamins and minerals. A grain of sand weighs approximately 50 mg.
• Pound (lb): The primary mass unit in the US customary system, defined as exactly 0.45359237 kg. Used for body weight, food products, and general commerce in the United States, Liberia, and Myanmar.
• Ounce (oz): One-sixteenth of a pound, equal to approximately 28.3495 grams. Used for food portions, postal weight, and product packaging in the US. Not to be confused with the troy ounce (31.1035 g) used for precious metals.
• US Ton (short ton): Equal to 2,000 pounds or 907.185 kilograms. Used in the United States for heavy materials like coal, grain, vehicles, and industrial products.
• Metric Ton (tonne, t): Equal to 1,000 kilograms or 2,204.62 pounds. The international standard for large-scale mass measurements in shipping, agriculture, and industry.
• Stone (st): Equal to 14 pounds or 6.35029 kilograms. Used primarily in the United Kingdom and Ireland for expressing body weight.

Step-by-Step Example

Convert 75 kilograms to all other mass units:

1. Start with: 75 kg
2. To grams: 75 x 1,000 = 75,000 g
3. To milligrams: 75 x 1,000,000 = 75,000,000 mg
4. To pounds: 75 x 2.20462 = 165.347 lb
5. To ounces: 75 x 35.274 = 2,645.55 oz
6. To US tons: 75 / 907.185 = 0.08267 tons
7. To metric tons: 75 / 1,000 = 0.075 t
8. To stone: 75 / 6.35029 = 11.811 st

A mass of 75 kilograms, which is roughly the weight of an average adult, equals about 165.3 pounds, 11.8 stone, or 75,000 grams. This conversion is commonly needed for international travel, medical records, and fitness tracking across different unit systems.

Practical Examples

Example 1: Emma's Baggage Weight Check

Emma is flying from New York to London and her airline has a 23 kg checked baggage limit. Her bathroom scale reads in pounds, and her suitcase weighs 48 pounds. She uses the mass calculator to check whether she is within the limit:

• Suitcase weight: 48 lb
• In kilograms: 21.77 kg
• Airline limit: 23 kg
• Remaining allowance: 23 - 21.77 = 1.23 kg (2.71 lb)

Emma's suitcase at 48 pounds (21.77 kg) is within the 23 kg limit with 1.23 kg to spare. She can add about 2.7 more pounds of items. She also notes that the UK often expresses weight in stone, so her 48-pound suitcase weighs 3 stone 6 pounds, which she finds useful for conversations with her British relatives.

Example 2: Chef Marco's Recipe Scaling

Chef Marco is adapting a French pastry recipe that calls for 250 g of butter and 175 g of sugar for his American kitchen, which uses ounces. He also needs to scale the recipe up by 3 times for a catering event:

• 250 g butter = 8.82 oz (approximately 8 7/8 oz)
• 175 g sugar = 6.17 oz (approximately 6 1/8 oz)
• Scaled up 3x: butter = 750 g = 26.46 oz (1 lb 10.46 oz)
• Scaled up 3x: sugar = 525 g = 18.52 oz (1 lb 2.52 oz)

Marco converts each ingredient from grams to ounces and then scales by 3. The total butter needed is 750 g (1 pound 10.5 ounces), and the total sugar is 525 g (1 pound 2.5 ounces). He rounds these to practical measuring amounts for his kitchen scale. Using the mass calculator ensures precision that preserves the delicate balance of the pastry recipe.

Example 3: Transport Company Weight Compliance

A transport company needs to ship 45 metric tons of steel from Germany to the United States. The US road weight regulations specify maximum loads in US tons. The logistics manager uses the mass calculator to ensure compliance:

• Shipment: 45 metric tons
• In US tons: 49.60 US tons
• In pounds: 99,208 lb
• US truck gross weight limit: 40 US tons (80,000 lb)

The 45 metric ton shipment equals 49.60 US tons (99,208 pounds), which exceeds the standard US truck gross weight limit of 80,000 pounds. The logistics manager splits the shipment into two trucks of 22.5 metric tons each (24.80 US tons or 49,604 lb per truck), both safely under the limit. This conversion prevented a potentially costly overweight violation.

Example 4: Dr. Patel's Medication Dosage

Dr. Patel needs to calculate a weight-based medication dosage for a patient who reports their weight as 12 stone 4 pounds. The dosage chart requires weight in kilograms at 5 mg per kg of body weight:

• Patient weight: 12 stone 4 lb = 172 lb
• In kilograms: 78.02 kg
• Dosage at 5 mg/kg: 78.02 x 5 = 390.1 mg
• In grams: 0.39 g

Dr. Patel converts the patient's weight from 12 stone 4 pounds to 78.02 kg and calculates the medication dosage as 390 mg. Accurate weight conversion is critical in medical dosing because even small errors can lead to under-dosing (ineffective treatment) or over-dosing (potential toxicity). The mass calculator ensures precise kg conversion from any starting unit.

Mass Conversion Reference Table

Standard conversion values. 1 stone = 14 lb = 6.35029 kg. 1 US ton = 2,000 lb = 907.185 kg. 1 metric ton = 1,000 kg = 2,204.62 lb.

Tips and Complete Guide

Quick Mental Conversion Shortcuts

For rapid mental conversions between kilograms and pounds, use the approximation that 1 kg is roughly 2.2 lb. To go from kg to lb quickly, double the number and add 10%. For example, 80 kg: doubled is 160, plus 10% (16) equals 176 lb (actual: 176.37 lb). To go from lb to kg, divide by 2 and subtract 10%. For example, 200 lb: halved is 100, minus 10% (10) equals 90 kg (actual: 90.72 kg). For stone to pounds, simply multiply by 14. For ounces to grams, multiply by 28 (actual factor is 28.35). These shortcuts are accurate to within 1% to 2% and are invaluable for quick estimates in shopping, cooking, fitness, and travel contexts where a calculator may not be convenient.

Mass Units Around the World

Different countries and contexts use different mass units. The kilogram is the global scientific standard and is used for everyday weighing in most countries. The United States uses pounds and ounces for most purposes, with tons for large quantities. The United Kingdom uses a mix: kilograms for food packaging (required by law since 2000), stone and pounds for body weight, and metric tons for industry. Japan uses kilograms but also the traditional momme (3.75 g) for pearl weight. India uses kilograms alongside traditional units like the tola (11.66 g) for gold. The gem industry uses carats (0.2 g). Precious metals use troy ounces (31.1 g). Pharmacies traditionally used grains (64.8 mg), though milligrams are now standard.

Precision and Accuracy in Mass Measurement

The precision needed for mass measurement varies enormously by application. Shipping logistics works in kilograms or tons with precision to the nearest kilogram. Cooking typically requires precision to the nearest gram or fraction of an ounce. Laboratory chemistry demands milligram or even microgram precision. Pharmaceutical manufacturing requires precision to fractions of a milligram. Analytical chemistry may need precision to micrograms (one millionth of a gram). When converting between units, maintain the same number of significant figures as your original measurement. A kitchen scale reading of 250 g should be reported as 8.82 oz, not 8.818490 oz, because the original measurement was only precise to three significant figures.

Common Mistakes to Avoid

• Confusing ounces with fluid ounces: An ounce (oz) is a unit of mass equal to 28.35 grams. A fluid ounce (fl oz) is a unit of volume equal to 29.57 mL. They measure completely different things. Eight ounces of flour by weight and 8 fluid ounces of flour by volume are not the same amount.
• Mixing up US tons and metric tons: A US (short) ton equals 2,000 lb (907.2 kg), while a metric ton equals 2,204.6 lb (1,000 kg). The 10% difference can be significant in large shipments. Always verify which "ton" is being referenced in contracts and specifications.
• Using troy ounces for non-precious metals: A troy ounce (31.1 g) is about 10% heavier than a regular (avoirdupois) ounce (28.35 g). Troy ounces are used exclusively for precious metals and gemstones. Using the wrong ounce for gold or silver calculations leads to pricing errors.
• Rounding too early in multi-step conversions: When performing multiple conversions in sequence, carry extra decimal places through intermediate steps and round only the final result. Early rounding accumulates errors that can become significant, especially with very large or very small quantities.
• Forgetting that stone includes remaining pounds: Body weight in stone is expressed as stone and pounds, not decimal stone. A person weighing 165 lb is 11 stone 11 lb (11 x 14 = 154, with 11 remaining), not 11.79 stone in everyday usage.

Frequently Asked Questions