The perceived ‘difficulty’ of a word is often about how familiar it is to the reader.

It is hard to say exactly which words are likely to be familiar to adult readers, because of individual differences in language skills, reading ability, education, professional training and employment.

But a general measure of the familiarity of words is their frequency in common reading material, such as newspapers. Lists of more common words and their frequencies are available from international reference databases such as CELEX, or dictionaries for learners of English as a second language, such as the Longman dictionary of contemporary English. Dictionaries for learners of English as a second language try to define only the 3,000 most commonly used words, so that they are as useful as possible for those with limited vocabularies.

You can check the vocabulary range of your text against such resources.