Carats to Stones Converter - Convert ct to st
Convert precisely with st = (ct × 0.0002) ÷ 6.35029318 (i.e., st = ct ÷ 31,751.4659). The reverse identity is ct = st × 31,751.4659. Very small or large outputs switch to scientific notation automatically for clarity.
Exact identities: 1 ct = 0.2 g = 0.0002 kg and 1 st = 14 lb = 6.35029318 kg. See all weight conversion calculators.
About Carats to Stones Conversion
The carat (ct) anchors gemstone trade and certification with an exact metric definition (0.2 g). The stone (st) is a traditional avoirdupois mass unit equal to 14 pounds, or exactly 6.35029318 kilogram. Converting from carats to stones bridges gemological measurements-typically used for single stones or SKUs-with regional and historical reporting that sometimes expresses larger masses in stones. Because both units have exact kilogram links, the mapping is deterministic and audit-ready.
In practice, laboratories and marketplaces weigh stones in carats or grams, while some consumer contexts (especially in the UK and Ireland) still reference stones for body mass or bulk items. A precise, invertible conversion ensures consistency across databases, certificates, and logistics documents-no guesswork, no compounding rounding drift. Store canonical values in SI (grams or kilogram) where possible, convert once for presentation, and keep unit symbols explicit wherever values appear in UIs and exports.
Carats to Stones Formula
Exact relationship
st = (ct × 0.0002) ÷ 6.35029318 = ct ÷ 31,751.4659
// inverse
ct = st × 31,751.4659Unit breakdown:
1 ct = 0.2 g = 0.0002 kg (exact) 1 st = 14 lb = 6.35029318 kg (exact)
⇒ 1 st = 31,751.4659 ct (exact) and 1 ct ≈ 0.000031496 stRelated Weight Converters
What are Carats (ct)?
A carat is the standardized mass unit for gemstones and pearls, defined as exactly 0.2 gram. It subdivides into points (1 point = 0.01 ct), which is convenient for small stones and grading notes. Because it is an exact metric definition, carat-based measurements integrate cleanly with SI pipelines for uncertainty budgets, analytics, and cross-border compliance. Total carat weight (tcw) aggregates stones for multi-stone settings and inventory summaries.
What are Stones (st)?
The stone is an avoirdupois mass unit equal to exactly 14 pounds. Using the international pound (0.45359237 kg), one stone equals exactly 6.35029318 kg. While less common in scientific calculation, stones remain part of cultural usage and some retail communications in specific regions. This converter employs the exact international definitions to ensure reproducibility across software and documents.
Do not confuse stones with troy units or short/long tons. Stones belong to the avoirdupois system; troy units are used for precious metals and are different quantities.
Step-by-Step: Converting ct to st
- Start with a mass in carats (ct).
- Multiply by 0.0002 to express the mass in kilogram (kg).
- Divide by 6.35029318 to convert kilogram to stones (st).
- Round once at presentation; retain full internal precision for exports and reconciliation.
Example walkthrough:
Input: 100,000 ct
Compute: kg = 100,000 × 0.0002 = 20 kg
st = 20 ÷ 6.35029318 ≈ 3.149606299 st
Output: ≈ 3.149606299 st (UI rounding only)Deep-Dive Use Cases
Appraisals and certification
Labs may store SI values for traceability, then present carats for trade and stones/kilogram for region-specific summaries. Exact factors ensure reproducible results across tools.
Inventory and logistics
Purchase orders and catalogs often speak in carats, while carriers or stakeholders may reference stones or kg. A deterministic ct → st bridge reduces manual edits and reconciliation risks.
Analytics and reporting
Warehouses can aggregate in SI, then pivot to stones for regional dashboards while still serving carats for SKU-level retail reporting-all from a single source of truth.
Common Conversions
| Carats (ct) | Stones (st) |
|---|---|
| 1 | 0.000031496 |
| 5 | 0.000157481 |
| 10 | 0.000314962 |
| 1,000 | 0.031496063 |
| 5,000 | 0.157480315 |
| 10,000 | 0.31496063 |
| 25,000 | 0.787401575 |
| 50,000 | 1.57480315 |
| 100,000 | 3.149606299 |
| 250,000 | 7.874015748 |
| 500,000 | 15.748031496 |
| 1,000,000 | 31.496062992 |
Quick Reference Table (Reverse)
| Stones (st) | Carats (ct) |
|---|---|
| 0.10 | 3,175.14659 |
| 0.25 | 7,937.866475 |
| 0.50 | 15,875.73295 |
| 1.00 | 31,751.4659 |
| 2.00 | 63,502.9318 |
| 5.00 | 158,757.3295 |
| 10.00 | 317,514.659 |
| 16.00 | 508,023.4544 |
| 32.00 | 1,016,046.9088 |
| 64.00 | 2,032,093.8176 |
| 100.00 | 3,175,146.59 |
Precision, Rounding & Significant Figures
Operational rounding
Compute with full precision and round once for the chosen output. In retail copy, carats are often shown to two decimals; for stones, use decimals aligned with decision thresholds. Avoid rounding mid-pipeline to prevent drift when chaining conversions (e.g., ct → kg → st).
Consistent documentation
Keep both identities close to examples (st = ct ÷ 31,751.4659 and ct = st × 31,751.4659). Use explicit unit symbols (ct, st) in headers and CSV export columns. Note whether masses are net stones only or include settings/packaging.
Where This Converter Is Used
- Retail and catalog pipelines that store SI or carat mass but must align with regional stone-based narratives.
- Compliance and insurance workflows that prefer SI evidence while quoting carats or stones in customer-facing descriptions.
- Data warehouses aggregating tcw across SKUs and providing stone-facing summaries for certain markets.
- Education and R&D where exact, invertible factors enable reproducible calculations and unit discipline.
Frequently Asked Questions
What is the exact formula to convert carats to stones?
Use st = (ct × 0.0002) ÷ 6.35029318. Since 1 metric carat = 0.2 gram = 0.0002 kilogram and 1 stone = 14 lb = 6.35029318 kilogram (exact), dividing the kilogram value by 6.35029318 gives stones. Equivalently, st = ct ÷ 31,751.4659 (exact).
How do I convert back from stones to carats?
Use ct = st × 31,751.4659. This follows from ct per stone = 6.35029318 kg ÷ 0.0002 kg per ct = 31,751.4659 ct per st (exact).
Are these constants exact or approximate?
Exact. The international avoirdupois pound is exactly 0.45359237 kg, the stone is exactly 14 lb, so 1 st = 6.35029318 kg is exact. The metric carat is exactly 0.2 g = 0.0002 kg. Therefore the factor 31,751.4659 ct per st is exact.
Is the stone used worldwide?
The stone (st) is most common in the UK and Ireland for body mass and some commodities. Many other regions use kilogram. This tool uses the international definitions so conversions are globally consistent.
Do negative or fractional carats convert correctly?
Yes. The relationship is linear and sign-preserving. Fractional carats (e.g., 0.07 ct) or negative deltas in balance logs convert proportionally to stones.
What anchor pairs help with quick checks?
1 st = 31,751.4659 ct (exact); 0.5 st = 15,875.73295 ct; 10,000 ct ≈ 0.314 st; 100,000 ct ≈ 3.149 st. These anchors help sanity-check results at a glance.
How should I round for labels, appraisals, and reports?
Keep full internal precision and round once at presentation. Because outputs in stones can be small, 3–4 decimals may be useful. Document rounding rules in your data dictionary.
Does locale formatting change the math?
No. Localization affects only how numbers appear (decimal symbol and digit grouping). The conversion arithmetic and constants remain the same.
What is the difference between stone and troy units?
Stone is an avoirdupois mass unit (14 lb). Troy units (e.g., troy ounce) are used for precious metals and are unrelated to the stone. This tool uses the stone (st) as 6.35029318 kg exactly.
Any mental math tips for ct → st?
Divide by ~32,000 to get a quick estimate, then add about 0.8% (since the exact divisor is 31,751.4659, slightly less than 32,000). For example, 100,000 ct ÷ 32,000 ≈ 3.125; adding ~0.8% gives ≈ 3.15 st (exact is 3.1496…).
What symbols should I keep consistent?
Use ct for carats and st for stones. Keep symbols consistent in headings, tables, exports, and API fields.
Is carat the same as karat?
No. Carat (ct) measures mass for gemstones. Karat (K/kt) measures gold purity. They are unrelated quantities.
Tips for Working with ct & st
- Memorize anchors: 1 st = 31,751.4659 ct; 0.5 st = 15,875.73295 ct; 100,000 ct ≈ 3.1496 st.
- Round once at presentation; store canonical SI values internally for analytics and audits.
- Normalize points (pt) to carats by dividing by 100 before converting to or from stones.
- Be explicit that “st” means the avoirdupois stone; avoid mixing with troy units or tons.