21 Carat to Stone
Quick answer
21 Carat (ct) equals
0.000661 st
To convert 21 Carats to Stones, multiply by 3.149461e-5. Therefore, 21 Carat (ct) equals 0.000661 Stone (st).
Formula: st = ct × 3.149461e-5. Calculation: 21 × 3.149461e-5 = 0.000661 st.
Convert Carat (ct) to Stone (st) online with our free unit converter. In mass, 1 ct = 3.149461e-5 st. Explore step-by-step conversion steps, mathematical formulas, and quick conversion reference tables below.
Worked example: converting Carat to Stone
- Step 1 — start with the formula. st = ct × 0.0000314946
- Step 2 — substitute your figure. 21 ct × 3.149461e-5
- Step 3 — read the result. 21 ct = 0.000661 st
- Step 4 — check it in reverse. ct = st × 31,751.4659 returns 20.9877 ct, which matches the figure you started with.
Mass Converter
26 units available
21 ct = 0.000661 st
Formula:
st = ct × 0.0000314946With your value: 21 ct = 0.00066139 st
How big is that?
Everyday references on a logarithmic scale, all expressed in carat so you can sanity-check the result.
Other Carat to Stone conversions
Carat to Stone Conversion Table
| Carat (ct) | Stone (st) |
|---|---|
| 0.5 | 1.574730e-5 |
| 1 | 3.149461e-5 |
| 2 | 6.298922e-5 |
| 5 | 0.000157 |
| 10 | 0.000315 |
| 15 | 0.000472 |
| 20 | 0.00063 |
| 25 | 0.000787 |
| 50 | 0.001575 |
| 100 | 0.003149 |
| 250 | 0.007874 |
| 500 | 0.015747 |
| 1000 | 0.031495 |
Stone to Carat Conversion Table
| Stone (st) | Carat (ct) |
|---|---|
| 0.5 | 15,875.73295 |
| 1 | 31,751.4659 |
| 2 | 63,502.9318 |
| 5 | 158,757.3295 |
| 10 | 317,514.659 |
| 15 | 476,271.9885 |
| 20 | 635,029.318 |
| 25 | 793,786.6475 |
| 50 | 1,587,573.295 |
| 100 | 3,175,146.59 |
| 250 | 7,937,866.475 |
| 500 | 15,875,732.95 |
| 1000 | 31,751,465.9 |
Where these values come from
Every factor on this page is traced to the document that defines it. See the full provenance dataset or our methodology.
Carat (ct)
Mass
The metric carat is exactly 200 mg, agreed internationally in 1907.
National Institute of Standards and Technology (US) · Reviewed 2026-07-01
Stone (st)
Mass
Traceable to the kilogram, defined by fixing the Planck constant at 6.626 070 15 × 10⁻³⁴ J·s. Avoirdupois masses derive from the 1959 international pound (0.453 592 37 kg exactly).
Source: BIPM, The International System of Units (SI), 9th edition, 2019 (updated 2024)
Bureau International des Poids et Mesures · Reviewed 2026-07-01
How to Convert Carat to Stone
To convert from Carat (ct) to Stone (st), multiply the value by 3.149461e-5.
Formula: st = ct × 0.0000314946
Reverse: ct = st × 31,751.4659
Step-by-Step Example
- Start with your value in Carat. For example: 5 ct
- Multiply by the conversion factor: 5 x 3.149461e-5
- The result is: 0.000157 st
Carat and Stone Relationship
This calculation facilitates standardized conversion between recognized units of mass. Since 1 Carat represents a fraction of a Stone (1 Stone ≈ 3.175e+4 Carats), the Stone is the larger measurement interval. Understanding the relationship between Carat and Stone is essential for accurate calculations in physics, engineering, commerce, and daily applications.
About Carat
The carat equals 200 milligrams and is the standard unit for measuring gemstone weight.
Fun Fact: The word "carat" comes from the carob seed, which was used as a balance weight in ancient gem trading.
Common uses of Carat: gemstones, diamonds, jewelry.
About Stone
The stone equals 14 pounds or about 6.35 kg. It is primarily used in the UK and Ireland for expressing body weight.
Fun Fact: The stone varied in weight depending on the commodity being weighed until it was standardized at 14 pounds in 1835.
Common uses of Stone: body weight (UK), agriculture.
Frequently Asked Questions
- What is 21 Carat in Stone?
- 21 Carat equals 0.000661 Stone.
- How many Stones are in 1 Carat?
- There are exactly 3.149461e-5 Stones in 1 Carat. This means the conversion factor from Carat to Stone is 3.149461e-5.
- What is the formula to convert Carat to Stone?
- The formula to convert Carat to Stone is: st = ct × 0.0000314946. For example, to convert 10 Carats to Stones, you would multiply 10 by 3.149461e-5.
- What is a Carat?
- The carat equals 200 milligrams and is the standard unit for measuring gemstone weight.
- What is a Stone?
- The stone equals 14 pounds or about 6.35 kg. It is primarily used in the UK and Ireland for expressing body weight.
- What are the common uses of Carat?
- The Carat is commonly used in gemstones, diamonds, jewelry.
Related Mass Conversions
Cite this page
UnitConvertLab. (2026). 21 Carat to Stone. UnitConvertLab. Retrieved from https://unitconvertlab.com/convert/21-carat-to-stone