As per the entry requirements, you need “C1 level on the Common European Framework”
C1 level on the CEFR is the same as IELTS Band 7.0 – 7.5 in all elements.
Therefore, you need a minimum of IELTS 7.0 to do the CELTA course if you are a non-native English speaker.
Check the CEFR for a full guide to English levels and equivalent test scores