How much does a 3.00 to 4.99ct I SI1 natural cushion diamond cost?

As of September 2026, 3.00 to 4.99ct I SI1 natural cushion diamonds typically cost £16,518 GBP to £47,217 GBP, with a median price of £27,041 GBP. There are currently 317 diamonds matching this specification available across retailers.

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

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3.00 to 4.99ct I SI1 Natural Cushion

Quick answer

As of September 2026, there are 317 natural cushion diamonds with I colour and SI1 clarity in the 3.00 to 4.99ct range available across retailers worldwide. Prices typically run £16,518 GBP to £47,217 GBP, with a median of £27,041 GBP. At least 47 retailers stock this exact specification. Half of all listings fall between £7,103 GBP and £10,084 GBP per carat. The same specification in lab grown form lists at a median of about £448 GBP per carat.

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

Caratlytics Diamond Price Index, August 2026: natural diamonds at 2,184 USD per carat and lab-grown at 464 USD per carat, a natural to lab ratio of 4.7 to 1. Cushion natural stones in the index: 2,792 USD per carat, +1.1% month on month. See the full index release

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

Last updated: September 2026

Available

317

Lowest Price

£7,195 GBP

Highest Price

£91,531 GBP

Average Price

£29,709 GBP