Gem size data: carat to mm tables to download (CSV and JSON)
By HeyGema™ · Updated
In short
The tables behind the HeyGema charts, free to download as CSV and JSON: diamond size by shape and carat, round size for 24 gems, mm to carat, US ring sizes and melee. Use them with a link back to the source (CC BY 4.0).
- Diamond size by shape and carat weight12 shapes, 0.1 to 100 carat: length, width, inches, face-up area.
- Round stone size by gem and carat weight24 gems with specific gravity, 0.1 to 50 carat: diameter in mm.
- Round diamond mm to carat1 to 20 mm in half steps: diamond weight and moissanite true weight.
- US ring sizes in mmSizes 3 to 13: inside diameter and circumference in mm and inches.
- Melee diamond sizes0.8 to 3.5 mm: weight of one stone and stones per carat.
- All of the above as JSONOne file with metadata, units and the method.
How to use the data
The data is licensed under Creative Commons Attribution 4.0: use it in articles, spreadsheets, shops and apps, and credit it with a link to HeyGema gem size charts. The sizes are estimates for a well-cut stone; read the methodology for the formulas and limits before you rely on a figure.
Columns
- diamond-size-by-shape-and-carat.csv
- Columns: shape, carat, length_mm, width_mm, length_in, width_in, ratio, faceup_area_mm2
- gem-round-size-by-carat.csv
- Columns: gem, specific_gravity, carat, diameter_mm
- round-mm-to-carat.csv
- Columns: diameter_mm, diamond_ct, moissanite_true_ct
- us-ring-sizes.csv
- Columns: us_size, inside_diameter_mm, inside_circumference_mm, inside_diameter_in
- melee-diamond-sizes.csv
- Columns: diameter_mm, weight_ct, stones_per_carat
Embed a chart on your site
Prefer a ready-made chart? Embed a size chart on your own page with one line of code.
Questions
Yes, under Creative Commons Attribution 4.0. Credit HeyGema with a link to the gem size charts.
By the method on the methodology page: reference sizes at 1 carat, cube root scaling by weight and density by gem.