Diamond Weight (Carat) Calculator

Estimate a round diamond's carat from its diameter.

Estimated weight (carats) 1

Formula: carat ≈ (diameter ÷ 6.5)³

Step-by-step with your numbers:

1. Values used:

2. Diameter = 6.5

4. Estimated weight = 1carats

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Estimate a round-brilliant diamond's carat weight from its diameter.

The math behind it

A 6.5 mm round brilliant is about 1 carat; weight scales with diameter cubed: carat ≈ (mm ÷ 6.5)³.

6.5 mm → ~1.0 carat.

Exact?

Cut depth and shape change it — this is an estimate for round brilliants.