Carats to Tonnes
An instant carats-to-tonnes converter, with the formula and a reference table below.
| Carats | Tonnes |
|---|---|
| 1 ct | 2e-07 t |
| 2 ct | 4e-07 t |
| 3 ct | 6e-07 t |
| 5 ct | 1e-06 t |
| 10 ct | 2e-06 t |
| 25 ct | 5e-06 t |
| 50 ct | 1e-05 t |
| 100 ct | 2e-05 t |
How to use
- Enter a value in the Carats field.
- The Tonnes figure appears immediately — no button to press.
- Typing in the Tonnes field converts back to Carats the same way.
- Use the reference table for the values that come up most often.
Carats to Tonnes formula
The factor from carats to tonnes is 2e-07.
t = ct × 2e-07
Why this factor: the carat and the tonne are both defined against the kilogram, so dividing one definition by the other gives 2e-07 directly. Both definitions are set out in full below.
To go the other way, divide by 2e-07 — or use the Tonnes to Carats converter, which is the same calculation reversed.
Worked example
Given 2 ct, multiplying by 2e-07 yields 4e-07 t.
2 ct × 2e-07 = 4e-07 t
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 tonne?
A tonne, or metric ton, is 1,000 kilograms — the standard unit for bulk freight and industrial quantities.
Definition: Exactly 1,000 kilograms. Accepted for use with SI but not itself an SI unit.
Where it is used: Shipping and freight, steel and cement output, vehicle masses, and carbon emissions accounting.
Worth knowing: Distinct from the US short ton (2,000 lb ≈ 907 kg) and the UK long ton (2,240 lb ≈ 1,016 kg).
Carats vs Tonnes
The carat is a specialized unit while the tonne is a metric 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 tonnes are in a carat?
One carat equals 2e-07 tonnes.
What is the formula to convert carats to tonnes?
Multiply the number of carats by 2e-07. To reverse it, divide by 2e-07 instead.
How do I convert tonnes back to carats?
Divide by 2e-07, which is the same as multiplying by 5000000.
How many tonnes are in 10 carats?
10 ct works out to 2e-06 t.
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.