The Model X is built on the same platform as the Model S and the SUV is expected to be about 10% heavier than the sedan. The ~10% bigger figure is consistent across most EPA ratings between the 2 vehicles.
Below the break you will find the EPA ratings of the Model X 90D and P90D compared to the Model S 90D and P90D:
The EPA has yet to release the ratings of the Model X 70D, which will be the less expensive version of the model. Tesla will launch the Model X on September 29th and is expected to deliver the first few Signature Model X’s at the event. All Signature Model X’s are P90D so the EPA has still some time to release official ratings for the lower-end version of the Model X.