Weight Converter Tools – Convert KG, LBS, Grams, Ounces, Stones, Tonnes, Carats, mg & µg
Welcome to the weight conversion hub—your one place to convert between kilograms, pounds, grams, ounces, stones, tonnes, carats, milligrams, and micrograms. Every tool uses exact, industry-standard constants and a mobile-first interface so you get instant, trustworthy answers.
Whether you’re preparing a recipe, printing a shipping label, documenting lab results, or listing gemstones for sale, consistent units matter. Our converters are designed to be predictable: we centralize precise constants, apply rounding only at display time, and keep the pages lightweight for speed.
For global teams, we recommend storing mass in SI units (typically kilograms or grams) and deriving regional representations like lb/oz and stones for display. This keeps analytics clean while ensuring customer-friendly interfaces. Each calculator below includes the exact formula, example walkthroughs, and practical guidance for rounding and documentation.
KG to LBS
Convert kilograms to pounds precisely.
LBS to KG
Convert pounds to kilograms (exact).
KG to Grams
Expand kilograms into grams accurately.
Grams to KG
Scale grams into kilograms instantly.
Grams to Ounces
Convert grams to ounces (avoirdupois).
Ounces to Grams
Translate ounces to grams for recipes & nutrition.
Pounds to Ounces
Break down pounds into ounces (1 lb = 16 oz).
Ounces to Pounds
Aggregate ounces into pounds accurately.
Pounds to Grams
Convert pounds to grams for labels & QA.
Grams to Pounds
Metric to US conversion with exact factors.
Kilograms to Ounces
Convert kilograms to ounces for small packs.
Ounces to Kilograms
Convert ounces to kilograms (exact).
KG to Stones
Convert kilograms to stones (UK/IE body weight).
Stones to KG
Convert stones to kilograms easily.
Pounds to Stones
Convert pounds to stones (14 lb = 1 st).
Stones to Pounds
Convert stones to pounds instantly.
Kilograms to Tonnes
Scale KG to metric tons for logistics & ops.
Tonnes to KG
Convert metric tons to kilograms (exact).
Milligrams to Grams
Convert mg to g for precise measurements.
Grams to Milligrams
Convert g to mg for medication & lab work.
Milligrams to Micrograms
Exact: 1 mg = 1000 µg (mcg).
Micrograms to Milligrams
Exact: mg = µg ÷ 1000.
Carats to Grams
Jewelry: convert ct to g (1 ct = 0.2 g).
Grams to Carats
Convert grams to carats for gemstones.
Why Exact Weight Conversions Matter
Small rounding differences create big problems when numbers pass through
multiple layers—browser UIs, PDFs, email invoices, CSV exports, and data
pipelines. By using exact constants—for example, 1 lb =
0.45359237 kg, 1 oz = 28.349523125 g, 1 stone = 14 lb, 1 tonne =
1000 kg—and rounding once at presentation, you keep every
surface in sync. That’s why each of our tools states the exact factor near
the calculator and repeats it in long-form guidance.
Core Relationships You’ll Use Daily
-
pounds = kilograms × 2.2046226218•kilograms = pounds × 0.45359237(exact) -
ounces = pounds × 16•pounds = ounces ÷ 16(exact) -
grams = ounces × 28.349523125•ounces = grams ÷ 28.349523125(exact) -
grams = kilograms × 1000•milligrams = grams × 1000•micrograms = mg × 1000(exact) -
stones = pounds ÷ 14•pounds = stones × 14(exact) -
kilograms = tonnes × 1000•tonnes = kilograms ÷ 1000(exact) -
carats = grams × 5•grams = carats × 0.2(exact metric carat)
Rounding, Precision & Display Strategy
Convert with full precision internally, then round once on output. For consumer-facing UIs, whole grams and one decimal place in ounces are typically enough. For nutrition labels and invoices, two decimals are common. For QA, R&D, and compounding, use additional decimals (up to the resolution of your measuring device) and document the policy in a short methods note. Consistency beats arbitrary precision.
Number formatting matters too. Use locale-aware thousands separators and decimal symbols, but never sacrifice the underlying numeric fidelity. Always pair numbers with clear unit symbols in table headers, axis labels, and CSV column names.
Data Modeling & Developer Tips
Choose a canonical unit like kg or g, name
fields explicitly (e.g., mass_kg,
mass_g, mass_lb), and keep conversions inside a shared
utility. This prevents silent changes and divergent math across services.
Maintain a small regression table of known pairs—such as “1 lb = 16 oz”,
“1 ct = 0.2 g”, “1 kg = 1000 g”—and test both directions to detect
accidental alterations in constants or formatting.
If you also show volume units, don’t blend them into mass tools. Conversions between mass and volume require density (and sometimes temperature), so keep those workflows separate and clearly labeled.
Regional Conventions & Accessibility
People in different regions think in different units. US shoppers often prefer pounds and ounces; UK and Irish audiences still reference stones for body weight; international logistics and research prefer SI units. Present the local unit while keeping SI canonical under the hood. For accessibility, ensure unit symbols are text (not images) and remain readable in high-contrast modes and screen readers.
Common Use Cases
- Fitness and health tracking (body weight in kg ⇄ lbs, stones ⇄ kg)
- Cooking and nutrition (grams ⇄ ounces for ingredients and labels)
- E-commerce and shipping (parcel weights in grams, kg, or lbs)
- Pharmacy and lab measurements (mg ⇄ g ⇄ µg for precise dosing)
- Jewelry and auctions (carats ⇄ grams with exact metric carat)
- Manufacturing, QA, and logistics (kg ⇄ tonnes; lb ⇄ oz for pick/pack)
Worked Examples
Shipping: A parcel is 1.875 lb. Multiply by 16 to get 30 oz exactly. If your label format uses whole ounces, display 30 oz; keep the exact value internally to avoid discrepancies when you also print kilograms.
Nutrition: A recipe calls for 250 g of flour. Divide by 28.349523125 to get ≈ 8.81849 oz. For a quick reference card, 8.82 oz is usually fine; for labelling, follow the governing standard’s rounding rules.
Jewelry: A stone weighs 0.316 g. Multiply by 5 to get 1.58 ct exactly. Display carats to two or three decimals per your policy; store grams (or milligrams) canonically in your database.
Frequently Asked Questions
Which weight unit should I use as my system’s single source of truth?
Pick one canonical unit—most teams choose kilograms or grams—and convert at the edges for user interfaces, reports, and exports. Centralizing the constant definitions and rounding policy prevents drift when values flow across emails, PDFs, dashboards, and APIs.
What are the exact mass constants I should rely on?
Use internationally fixed definitions: 1 lb = 0.45359237 kg; 1 oz (avoirdupois) = 28.349523125 g; 1 stone = 14 lb; 1 tonne (t) = 1000 kg; 1 kg = 1000 g; 1 g = 1000 mg; 1 mg = 1000 µg; 1 carat (ct) = 0.2 g. These constants are exact, so your results are reproducible on every device.
How should I round for labels, invoices, and dashboards?
Round once at presentation. For consumer UIs, whole grams or one decimal in ounces often suffice; for invoices, two decimals are common; for QA and lab work, 2–4 decimals or more may be required. The rule of thumb is: store full precision, round only on output.
What’s the difference between ounce (oz) and fluid ounce (fl oz)?
Ounce (oz) in our tools is a unit of mass; fluid ounce (fl oz) is a unit of volume for liquids. Do not interchange them unless you have density and a documented method to convert between mass and volume. Keep volume calculators separate from mass calculators.
Do I need separate tools for troy ounces?
Yes. Troy ounces—used for precious metals—are defined differently (1 troy oz = 31.1034768 g) and are not part of the everyday avoirdupois system. Mixing systems can lead to pricing and reporting mistakes, so troy conversions should live in a dedicated tool.
How can I ensure consistency across regions (US, UK, EU)?
Keep SI (kg, g) canonical in storage and derive pounds, ounces, and stones for regional displays. Publish your constants and rounding policy in a short methods note so every team member and integration uses identical math.
What are common mistakes that cause discrepancies in reports?
Frequent pitfalls include double-rounding at multiple layers, mixing mass ounces with fluid ounces, and using approximate constants. Another trap is storing mixed units in the same column; instead, store a canonical unit and derive the others on render.
When should I use stones?
Stones are mainly used for body weight in the UK and Ireland (1 st = 14 lb). If your product targets those regions, including stone conversions improves comprehension while you keep kg as the storage standard.
Why do some carriers request ounces while others use pounds or kilograms?
Parcel carriers in the US often accept both pounds and ounces for small packages, while customs and international documentation prefer grams or kilograms. Our tools let you convert precisely so labels, declarations, and catalogs agree.
How do carats relate to grams and milligrams?
The modern metric carat is exactly 0.2 g (200 mg). Jewelers also use “points,” where 1 ct = 100 points. In data models, keep grams or milligrams canonical and derive carats for certificates and storefronts.
Can I convert mass directly to volume without density?
No. Mass (g, kg) and volume (mL, L) are different physical quantities. To convert between them you need density at a stated temperature (and sometimes concentration). Keep density-driven workflows separate from pure unit conversions.
What precision should I target for mg and µg converters?
For supplements and nutrition, whole micrograms or one decimal often suffice. For compounding and analytical chemistry, 0.1 µg or better may be required by SOPs. Always store raw values with maximal fidelity and round once at presentation.
Is there a quick way to sanity-check conversions?
Maintain a small regression set of known pairs—like 1 lb = 16 oz; 1 kg = 1000 g; 1 ct = 0.2 g; 1 oz ≈ 28.349523125 g—and unit test both directions. This catches rounding errors and accidental constant changes early.
What about internationalization (i18n) and number formats?
Use locale-aware formatting for thousands separators and decimals, but keep the underlying numeric precision intact. Always specify units in labels and table headers so numbers are unambiguous across languages.
How should I name fields in analytics and exports?
Use explicit, unit-suffixed names like mass_kg, mass_g, mass_lb. Include a methods note in your documentation, e.g., “Exact constants: 1 lb = 0.45359237 kg; round once at presentation.” Clear naming prevents costly confusion later.
Keep This Page Handy
Bookmark this category page for rapid access to every weight converter on MetricCalc. As we expand the library, new tools will follow the same layout and rounding philosophy so you can switch units without relearning the interface. If you spot a unit we should add, let us know and we’ll build it using the same exacting standards.