In many circumstances organisers need a conversion of ECF rating to that of FIDE or vice versa. The ECF will be moving to a new conversion and will be recommending that conversion to other users.
On the 1st March 2024, FIDE is making changes to its ratings, increasing the rating floor from 1000 to 1400 and condensing all ratings between 1000 to 2000 into the new range. ECF ratings are not changing. Until this point the ECF ratings (and previously grades) followed a fairly clear linear relationship albeit people have suggested slightly different fits. This is now not the case.
The revised conversion after the FIDE change will be FIDE = 0.6xECF +700 up to 1750ECF with parity above that level.
The fit has been chosen to be minimally biased so it can be used in both directions while being reasonably practical. It can be seen to be one of many plausible interpretations.
The diagram demonstrates the formula on background of the latest data. The data is taken as at 2023 year end and plots all the players with an active FIDE rating (uprated for the 1st March change) and full ECF ratings.
From past experience the relationship can move around and so the rating team will review the recommendation from time to time.