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

As of October 2026, 1.50 to 1.99ct I SI1 natural round diamonds typically cost £3,008 GBP to £8,532 GBP, with a median price of £4,946 GBP. There are currently 1,600 diamonds matching this specification available across retailers.

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

About 40% of these diamonds are available at multiple retailers, with an average price spread of 47%. A comparison tool like Carat Hunter lets you see all the prices side by side.

1.50 to 1.99ct I SI1 Natural Round

Quick answer

As of October 2026, there are 1,600 natural round diamonds with I colour and SI1 clarity in the 1.50 to 1.99ct range available across retailers worldwide. Prices typically run £3,008 GBP to £8,532 GBP, with a median of £4,946 GBP. At least 68 retailers stock this exact specification, and 40% of the stones appear at more than one of them, with an average price spread of 47%. Half of all listings fall between £2,803 GBP and £4,462 GBP per carat. The same specification in lab grown form lists at a median of about £792 GBP per carat. Over the last 30 days the median price moved -2.2% and the number of listings moved +17.0%.

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. Round natural stones in the index: 2,248 USD per carat, +7.6% 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

1,600

Lowest Price

£1,510 GBP

Highest Price

£15,550 GBP

Average Price

£5,410 GBP