Best Princess Cut Diamond Ratio: What Buyers
Should Know

A diamond’s ratio is the length divided by the width of the stone. For princess cut diamonds, this measurement determines whether the diamond looks perfectly square or slightly rectangular.

For example:

• A diamond measuring 6.00 mm × 6.00 mm has a ratio of 1.00
• A diamond measuring 6.20 mm × 6.00 mm has a ratio of 1.03

Because princess cuts are traditionally square, ratio plays a much bigger role here than it does for elongated shapes.

This range creates a diamond that looks balanced, symmetrical, and visually appealing when set in an engagement ring.

Ratio Breakdown:

• 1.00 – 1.02
  Perfectly square appearance. Ideal for buyers who want classic symmetry.
• 1.03 – 1.05
  Slightly elongated but still square to the eye. Very popular and widely accepted.
• Above 1.05
  Noticeably rectangular. Typically avoided unless intentionally desired.

Most buyers prefer diamonds between 1.00 and 1.03 for the cleanest square look.

Princess cut diamonds are defined by their square shape. Ratios outside the ideal range can make the diamond look uneven or unbalanced once set.

A well-proportioned ratio ensures:

• Clean, symmetrical corners
• Even distribution of sparkle
• A polished, intentional look

Princess cut diamonds are brilliant-cut stones, meaning they rely on precise proportions to reflect light properly.

Poor ratios are often linked to:

• Light leakage
• Dark areas under the table
• Reduced brilliance

While ratio alone doesn’t determine sparkle, it’s a strong indicator of overall cut balance.

Diamonds within the ideal ratio range sit more naturally in popular settings like:

• Solitaire
• Halo
• Hidden halo
• Three stone

A poorly proportioned diamond can appear crooked or misaligned when set.

While ratio is important, it should never be evaluated alone.

Two diamonds with the same ratio can perform very differently depending on:

• Depth percentage
• Table size
• Pavilion angles
• Overall symmetry

Because GIA does not assign a formal cut grade to princess cut diamonds, buyers must evaluate ratio along with visual performance.

The best approach is choosing a princess cut diamond within the ideal ratio range that also appears bright and lively across the entire surface.

To support the ideal ratio, most well-cut princess diamonds fall within these ranges:

• Depth: ~65% – 75%
• Table: ~62% – 70%

Diamonds that are too shallow or too deep may lose sparkle even if the ratio is technically acceptable.

Within the ideal ratio range, face-up size differences are subtle. However:

• A perfectly square diamond (1.00–1.02) often looks more balanced
• A slightly elongated diamond (1.03–1.05) can appear marginally larger from certain angles

The difference is minimal, so buyers should prioritize symmetry and sparkle over size perception.

Focusing Only on Carat Weight

Two princess cut diamonds with the same carat weight can look very different if their ratios vary.

Ignoring Corner Alignment

Poor ratios often come with uneven corners, which affects both appearance and durability.

Choosing a Rectangular Princess Cut by Accident

Ratios above 1.05 may no longer look square, which surprises many buyers after setting.

For engagement rings specifically, the most recommended ratio is:

1.00 – 1.03

This range delivers:

• Classic square appearance
• Strong sparkle
• Better compatibility with wedding bands
• A timeless look that won’t feel trendy

This is why most curated princess cut engagement rings are selected within this ratio range.

Princess cut diamonds have sharp corners, which require protection. While ratio does not directly affect durability, extreme proportions can increase vulnerability.

Best practices include:

• Choosing a balanced ratio
• Using V-prongs or double prongs
• Avoiding overly shallow stones

A well-cut diamond with the right ratio and proper setting is suitable for everyday wear.

Both lab grown and natural princess cut diamonds follow the same ideal ratio guidelines.

However, lab grown diamonds offer:

• More flexibility in selecting ideal ratios
• Better access to high symmetry
• Greater value at larger carat sizes

This makes lab grown princess cut engagement rings especially popular with value-focused buyers.