Grams to Carats Converter — Convert g to ct (Exact: ct = g × 5)
Accurate grams (g) to carats (ct) converter using the exact metric carat definition 1 ct = 0.2 g (200 mg). Built for jewelry, gemstones, assay reports, auctions, and lab documentation. Includes formula, step-by-step examples, precision/rounding guidance, expanded quick tables, and in-depth FAQs.
Exact factor: 1 ct = 0.2 g (200 mg) ⇒ ct = g × 5. See all free weight converter calculator.
About Grams to Carats Conversion
The gram (g) anchors SI-based workflows—shipping, customs, inventory, and analytics—because it rolls cleanly to milligrams and kilograms. The carat (ct)—defined exactly as 0.2 g—remains the universal mass unit for gemstones across retail, auctions, and gemological labs. Converting grams to carats bridges scientific storage with jewelry-facing presentation without duplicating fields or introducing rounding drift.
Because 1 ct = 0.2 g is exact, systems can store mass canonically in grams (or milligrams) and compute carats at the edges for product cards, certificates, and invoices. Rounding once at display time keeps your dashboards, PDFs, and CSV exports aligned. For multi-region stacks, document constants and rounding in a short methods note so everyone uses the same math.
Remember that carats indicate weight, not size. If your workflow depends on mount compatibility or visual balance, pair carat weight with calibrated dimensions (mm) and, where relevant, note the stone’s specific gravity and cut proportions for accurate expectations.
Grams to Carats Formula
Exact relationship
Use either expression:
ct = g × 5
// reverse
g = ct × 0.2Example:
0.316 g × 5 = 1.58 ctRelated Weight Converters
What is a Gram (g)?
A gram is an SI unit of mass equal to 1/1000 of a kilogram. It appears in shipping labels, customs forms, lab notebooks, and e-commerce specs. Storing mass in grams (or milligrams) provides clean rollups to kilograms, simple arithmetic for BOMs, and exact derivations to carats, ounces, and pounds for customer-facing surfaces.
What is a Carat (ct)?
A carat is a gemstone mass unit equal to 0.2 g (200 mg). Trade also uses “points,” where 100 points = 1 ct. Certifications, price lists, and retail inventory are indexed by carat because it aligns with how stones are evaluated and sold. For manufacturing and analytics, keep SI as canonical and derive ct and points for presentation and search.
Step-by-Step: Converting g to ct
- Read the mass in grams (g).
- Multiply by 5 to convert to carats (ct).
- Apply your rounding policy once at presentation (e.g., ct to 2–3 d.p., g to 3–4 d.p.).
Example walkthrough:
Input: 0.55 g
Compute: 0.55 × 5 = 2.75 ct
Output: 2.75 ct (UI, 2-decimal rounding)Common Conversions
Everyday quick checks (g → ct)
| g | ct | g | ct |
|---|---|---|---|
| 0.010 | 0.05000 | 0.025 | 0.12500 |
| 0.050 | 0.25000 | 0.066 | 0.33000 |
| 0.100 | 0.50000 | 0.150 | 0.75000 |
| 0.200 | 1.00000 | 0.250 | 1.25000 |
| 0.300 | 1.50000 | 0.400 | 2.00000 |
| 0.500 | 2.50000 | 0.750 | 3.75000 |
| 1.000 | 5.00000 | 1.500 | 7.50000 |
| 2.000 | 10.00000 | 3.000 | 15.00000 |
| 5.000 | 25.00000 | 10.000 | 50.00000 |
| 20.000 | 100.00000 | 50.000 | 250.00000 |
Precision, Rounding & Significant Figures
Operational rounding
Retail: 0.01–0.001 ct and 3–4 d.p. in grams are common. Lab/certificates may require tighter tolerances. Store raw values with full precision; round once at output to maintain auditability across invoices, certificates, and dashboards.
Consistent documentation
Name fields clearly (e.g., mass_g, mass_ct, mass_mg) and add a methods note: “Conversion uses 1 ct = 0.2 g (exact); ct = g × 5; g = ct × 0.2. UI shows ct to 2–3 decimals; g to 3–4 decimals.”
Where This Converter Is Used
- 💎 Jewelry retail & auctions: Present carats to buyers while warehousing and shipping in grams.
- 🧪 Gem labs & appraisals: Certificates that report ct with gram/mg precision internally.
- 🏭 Manufacturing: Casting, settings, and QC that reconcile ct to SI units for BOMs and audits.
- 📦 Logistics & customs: Declarations and harmonized codes that prefer SI mass (g/kg).
- 📊 Analytics: Price-per-carat datasets normalized in grams for cross-category analysis.
Quick Reference Table
Common carat values (ct → g)
| ct | g | ct | g |
|---|---|---|---|
| 0.10 | 0.02000 | 0.25 | 0.05000 |
| 0.33 | 0.06600 | 0.50 | 0.10000 |
| 0.75 | 0.15000 | 1.00 | 0.20000 |
| 1.25 | 0.25000 | 1.50 | 0.30000 |
| 2.00 | 0.40000 | 2.50 | 0.50000 |
| 3.00 | 0.60000 | 5.00 | 1.00000 |
| 7.50 | 1.50000 | 10.00 | 2.00000 |
| 20.00 | 4.00000 | 50.00 | 10.00000 |
| 100.00 | 20.00000 | 250.00 | 50.00000 |
Frequently Asked Questions
What is the exact formula to convert grams to carats?
Use the metric carat definition adopted internationally: 1 carat (ct) = 200 milligrams = 0.2 grams. Since 1 g equals 5 ct, multiply grams by 5 to get carats: ct = g × 5. The inverse is g = ct × 0.2. Because this relationship is exact (not approximate), you can standardize rounding—e.g., show ct to 2–3 decimals for retail and g to 3–4 decimals for lab work—while keeping full precision internally for consistency across UI, PDFs, and exports.
Is carat (ct) the same as karat (kt)?
No. Carat (ct) measures MASS of gemstones; karat (kt or K) measures PURITY of gold alloys (24 kt = pure gold). Mixing them causes misinterpretation and potentially costly errors. Keep symbols and field names distinct in your data model (e.g., mass_ct vs. gold_karat) and in your UI labels and exports.
Do carats measure size or weight? Why can two 1 ct stones look different?
Carats measure mass. Apparent size depends on gemstone density (specific gravity) and cut proportions. A 1 ct diamond and a 1 ct sapphire have different volumes and face-up sizes because densities differ. Likewise, a deep cut concentrates mass below the girdle and can make the face-up diameter smaller at the same carat weight. Use carats for weight and certifications; use calibrated dimensions (mm) for settings and design.
What precision should I display for grams and carats in retail vs. laboratory contexts?
Retail listings commonly show ct to two decimals (e.g., 1.23 ct), sometimes three for fine stones. Appraisals and labs often use three decimals in ct and 3–4 decimals in grams. Best practice: store mass in grams (or milligrams) with full precision, derive carats for display, and round once at the output boundary. Publish a short methods note with constants and rounding to keep invoices, certificates, and dashboards aligned.
How do points relate to carats and grams?
Jewelers also use “points,” where 1 ct = 100 points. That means 0.01 ct = 1 point, 0.25 ct = 25 points, 1.50 ct = 150 points, etc. With 1 ct = 0.2 g, each point equals 0.002 g (2 mg). For modeling, keep grams or milligrams canonical, and derive ct and points for UI to avoid floating-point drift in analytics.
Show a worked example with rounding.
Suppose a gem weighs 0.316 g. Convert to carats: ct = 0.316 × 5 = 1.58 ct exactly. If the site shows two decimals, display 1.58 ct; if your grams display uses three decimals, show 0.316 g. Store the full-precision value and round only once when rendering to prevent tiny mismatches between labels, receipts, and CSV exports.
Any QA and audit tips for jewelry workflows?
Centralize unit conversions; write unit tests for known pairs (e.g., 1 ct = 0.2 g; 2.5 ct = 0.5 g; 5 ct = 1.0 g; 0.316 g = 1.58 ct). Ensure your scales are calibrated and that your UI indicates resolution (e.g., 0.001 g). Include unit symbols in every table and export, and log constants in a methods note: “Exact: 1 ct = 0.2 g (200 mg); ct = g × 5; g = ct × 0.2.”
Tips for Working with Grams & Carats
- Keep SI canonical (g/mg); compute ct and points at the edge for storefronts and certificates.
- Publish a single rounding policy (e.g., ct: 0.01–0.001; g: 3–4 d.p.) and apply it consistently.
- Don’t confuse carat (mass) with karat (purity); enforce distinct field names and symbols.