Mass conversion formula

Mass conversion is really just a multiplier problem. Every mass unit has a fixed relationship to a reference unit. In the international system (SI), the reference unit is the kilogram (kg). So the easiest way to convert any unit A to any unit B is:

• Convert A to kilograms: kg = value × factorToKg(A)
• Convert kilograms to B: valueB = kg ÷ factorToKg(B)

That’s it. No complicated equations, no approximations needed. If you know each unit’s exact conversion factor to kilograms, you can convert between any two units. This calculator stores those factors and does the two-step conversion instantly.

• It avoids maintaining a huge table of every possible pair conversion.
• It reduces rounding error because there’s a single, consistent base.
• It matches how most scientific and engineering references define conversions.

Most mass conversions are exact ratios (for example, 1 pound is defined as exactly 0.45359237 kilograms). In real life, the number of decimals you show depends on your use case. For cooking, 1–2 decimals is often enough. For shipping or gym tracking, 2–3 decimals can be useful. For lab work, you may need more — and you should follow your lab’s significant-figures rules.

Real-world conversion examples

Here are practical conversions that come up constantly. You can copy these, but it’s even better to run them here and screenshot the result for quick reference.

Suppose you have 2.5 kg and want pounds. Using the definition 1 lb = 0.45359237 kg: first convert to kg (already in kg), then divide by 0.45359237. The calculator returns approximately 5.5116 lb.

Convert 100 g to ounces. Since 1 oz = 0.028349523125 kg and 100 g = 0.1 kg, we compute 0.1 ÷ 0.028349523125 ≈ 3.5274 oz. That’s why 100 grams is often remembered as “about 3.5 ounces”.

In the UK, body weight is sometimes written in stones (st). 1 stone = 14 lb. So 10 st is 140 lb, and that’s 140 × 0.45359237 ≈ 63.5029 kg.

A tonne (metric ton) equals 1000 kg. To get pounds, convert 1000 kg to lb: 1000 ÷ 0.45359237 ≈ 2204.6226 lb.

What this Mass Converter does (step-by-step)

When you click Convert, the calculator runs a simple pipeline designed for both accuracy and “shareability”:

• It checks that you entered a numeric value.
• It checks that you picked a From unit and a To unit.
• If something is missing, it highlights the field and shows a clear error message.

Every unit has a “to kilograms” factor. For example, grams (g) have a factor of 0.001 because 1 g = 0.001 kg. Pounds (lb) have a factor of 0.45359237 because 1 lb = 0.45359237 kg.

Once the value is in kg, converting to the target is just dividing by the target unit’s factor. This yields your final output in the unit you requested.

The calculator formats the result so it’s easy to read and easy to paste. It avoids scientific notation for common ranges, trims unnecessary trailing zeros, and shows a friendly sentence you can copy into homework, recipes, gym logs, or shipping forms.

• Swap: flip the From/To units instantly (great for “1 lb → kg” and “1 kg → lb”).
• Copy: copy the output sentence to your clipboard.
• Share: share to WhatsApp, Telegram, X, Facebook, LinkedIn, or the native share sheet.
• Save: store conversions locally so you can compare later (like a mini history log).

Frequently Asked Questions

• Is “mass” the same as “weight”?

  In physics, mass and weight are different: mass is the amount of matter, and weight is the force due to gravity. In everyday life (recipes, shipping, gym, packages), people often use “weight” to mean mass in these units. This calculator converts the units themselves (kg, lb, oz, g), which are commonly used as “weight” in daily contexts.

• Are the conversions exact?

  The underlying relationships are defined as fixed ratios (for example, the international avoirdupois pound is defined as exactly 0.45359237 kg). The only “non-exact” part is how many decimals you choose to display or copy.

• Why do I see slightly different decimals on other sites?

  Differences usually come from rounding (fewer decimals), using an approximation, or converting via an intermediate unit that adds extra rounding steps. This calculator converts via kilograms in one consistent pass.

• Which units are included?

  This converter includes metric units (mg, g, kg, tonne), common US/UK units (oz, lb, stone, US ton, UK long ton), and smaller specialty units (carat, grain). If you need another unit, you can add it by defining its factor to kilograms.

• Can I convert “1 lb of feathers” vs “1 lb of steel”?

  Yes — and the answer is the same: 1 lb is 1 lb regardless of material. People joke about this because feathers look bigger, but the mass unit doesn’t change.

• Do you store my values online?

  No. The conversion runs locally in your browser. If you click Save, the history is stored locally on your device using your browser’s storage — not uploaded to a server.