Diamond Proportions and Measurements Guide

Diamond proportions show where the weight sits and how the facets work together. They are a screening system, not a beauty grade. Start with the GIA report, compare the relationships, then make the actual diamond prove the numbers.

By Rob Cornfield, Co-Founder of YourDiamondGuys.com. More than 30 years in the global diamond trade. Specialist in diamond cut and light performance.

The report can look safe while the stone looks small, dark, windowed, or uneven. I have watched cutters save a carat threshold by leaving weight where the buyer cannot see it. Millimeters expose that decision. Video tells you what it did to the diamond.

Measurements, depth, outline, and light return work as one decision system.

Start With The Report

Report check

Read Length, Width, And Depth

See which millimeters control the face up footprint and which number reveals vertical weight.

Report check

Calculate Length To Width Ratio

Turn the first two measurements into a ratio, then check whether the outline actually supports it.

Report check

Pair Table Size With The Crown

Understand why a table percentage only works when the crown and pavilion support the same result.

Report check

Test Depth, Spread, And Performance

Find weight hidden below the girdle without rewarding a shallow diamond that leaks light.

Read The Diamond Architecture

Architecture check

Crown Height And Crown Angle

Use crown geometry to judge the opportunity for fire, spread, and a balanced angle pair.

Architecture check

Pavilion Depth And Pavilion Angle

See why the pavilion controls light return and why shallow and steep stones fail differently.

Architecture check

Total Depth Versus Pavilion Depth

Separate two report measurements that answer different buyer questions.

Architecture check

Girdle Thickness

Balance durability, setting security, and the cost of weight carried around the edge.

Architecture check

Culet Visibility

Judge modern and antique cuts differently when the bottom facet shows through the table.

Architecture check

Spread Score

Compare face up size inside a fair peer group without turning one number into a cut grade.

Architecture check

Outline Quality

Check symmetry, shoulders, bellies, points, corners, and the centerline the report cannot grade.

Architecture check

Fancy Shape Proportion Limits

Learn why matching table and depth percentages can still produce completely different diamonds.

Check Proportions By Shape

Shape check

Oval Proportions

Check outline, bow tie, belly depth, ratio, and spread in motion.

Shape check

Pear Proportions

Judge shoulders, belly, point alignment, bow tie, and tip durability as one shape.

Shape check

Emerald Cut Proportions

Reject windowing first, then compare ratio, step pattern, corners, and spread.

Shape check

Cushion Proportions

Identify chunky or crushed facet style before trying to compare the numbers.

Shape check

Radiant Proportions

Separate crisp mixed cut texture from a dark or mushy crushed pattern.

Shape check

Princess Proportions

Check square outline, pavilion bulge, fire, and corner protection before price.

Demand Proof

Proof check

Hearts And Arrows Precision Metrics

Verify pattern alignment, image capture, and optical symmetry instead of trusting a label.

Proof check

Proportion Red Flags Checklist

Run a fast report and visual triage before a diamond reaches the final shortlist.

Diamond Cut, Proportions, and Crown Height: What a Pro Sees First

Questions? Reach out directly for a free consultation, or drop them in the Diamond Buyers Academy community — Rob and Josh answer personally.