How much does a 1.50 to 1.99ct I SI1 natural cushion diamond cost?

As of October 2026, 1.50 to 1.99ct I SI1 natural cushion diamonds typically cost £2,296 GBP to £6,469 GBP, with a median price of £3,823 GBP. There are currently 445 diamonds matching this specification available across retailers.

Where can I find the best price on a I SI1 cushion diamond?

About 34% of these diamonds are available at multiple retailers, with an average price spread of 55%. A comparison tool like Carat Hunter lets you see all the prices side by side.

1.50 to 1.99ct I SI1 Natural Cushion

Quick answer

As of October 2026, there are 445 natural cushion diamonds with I colour and SI1 clarity in the 1.50 to 1.99ct range available across retailers worldwide. Prices typically run £2,296 GBP to £6,469 GBP, with a median of £3,823 GBP. At least 63 retailers stock this exact specification, and 34% of the stones appear at more than one of them, with an average price spread of 55%. Half of all listings fall between £2,129 GBP and £3,655 GBP per carat. The same specification in lab grown form lists at a median of about £462 GBP per carat. Over the last 30 days the median price moved -1.8% and the number of listings moved +7.7%.

Three of the best scored stones at this specification right now:

Caratlytics Diamond Price Index, September 2026: natural diamonds at 2,335 USD per carat and lab-grown at 443 USD per carat, a natural to lab ratio of 5.3 to 1. Cushion natural stones in the index: 2,948 USD per carat, +1.7% month on month. See the full index release

Figures come from current listings across more than 100 retailers and refresh daily. The index is a monthly release.

Last updated: October 2026

Available

445

Lowest Price

£1,463 GBP

Highest Price

£13,473 GBP

Average Price

£4,158 GBP