Carats to Stones
An instant carats-to-stones converter, with the formula and a reference table below.
| Carats | Stones |
|---|---|
| 1 ct | 3.14946e-05 st |
| 2 ct | 6.29892e-05 st |
| 3 ct | 9.44838e-05 st |
| 5 ct | 0.000157 st |
| 10 ct | 0.000315 st |
| 25 ct | 0.000787 st |
| 50 ct | 0.001575 st |
| 100 ct | 0.003149 st |
How to use
- Enter a value in the Carats field.
- The Stones figure appears immediately — no button to press.
- Typing in the Stones field converts back to Carats the same way.
- Use the reference table for the values that come up most often.
Carats to Stones formula
Converting carats to stones is a single multiplication by 3.14946089e-05.
st = ct × 3.14946089e-05
Why this factor: the carat and the stone are both defined against the kilogram, so dividing one definition by the other gives 3.14946089e-05 directly. Both definitions are set out in full below.
To go the other way, divide by 3.14946089e-05 — or use the Stones to Carats converter, which is the same calculation reversed.
Worked example
Given 25 ct, multiplying by 3.14946089e-05 yields 0.000787 st.
25 ct × 3.14946089e-05 = 0.000787 st
The converter above does this for any value you type, in either direction.
What is a carat?
A metric carat is the standard mass unit for gemstones.
Definition: Exactly 200 milligrams — that is, 0.2 gram — standardized internationally in 1907.
Where it is used: Diamond and gemstone weight throughout the jewellery trade.
Worth knowing: Do not confuse the carat (gemstone mass) with the karat (gold purity out of 24). A 1-carat diamond and 24-karat gold measure entirely different things.
What is a stone?
A stone is fourteen pounds, still the customary unit for body weight in Britain and Ireland.
Definition: Fourteen avoirdupois pounds, so exactly 6.35029318 kilograms.
Where it is used: Personal body weight in the UK and Ireland, where weight is usually given as stones and pounds.
Worth knowing: Effectively unused in the United States, where body weight is quoted in pounds alone.
Carats vs Stones
The carat is a specialized unit while the stone is an imperial unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many stones are in a carat?
One carat equals 3.14946089e-05 stones.
What is the formula to convert carats to stones?
Multiply the number of carats by 3.14946089e-05. To reverse it, divide by 3.14946089e-05 instead.
How do I convert stones back to carats?
Divide by 3.14946089e-05, which is the same as multiplying by 31751.4659.
How many stones are in 10 carats?
10 ct works out to 0.000315 st.
Is there anything to watch out for with carats?
Do not confuse the carat (gemstone mass) with the karat (gold purity out of 24). A 1-carat diamond and 24-karat gold measure entirely different things.
How is the carat defined?
Exactly 200 milligrams — that is, 0.2 gram — standardized internationally in 1907.