The ideal length for an email to achieve the highest response rates is between 50 and 125 words.
This has been proven in various studies, with emails in this range consistently achieving response rates above 50%. It's important to note, however, that the sweet spot for email length is not a hard and fast rule. While response rates do decline slowly after 125 words, they don't drop significantly until around the 500-word mark. After that, response rates remain fairly flat until around 2000 words, at which point they begin to decline rapidly.
It's also worth noting that extremely short emails, those under 50 words, have been shown to have a steep decline in response rates.
Emails with 25 words or less have a response rate that is comparable to emails with 2000 words or more. And emails with subject lines only, but no content in the body, have the lowest response rate of all, with only 11% receiving a response.
In terms of the reading level of emails, those written at a 3rd-grade level have been found to have the highest response rates, providing a 36% lift over emails written at a college reading level and a 17% higher response rate than emails written at a high school reading level. Additionally, emails that are slight to moderately positive or negative tend to elicit 10-15% more responses than completely neutral emails.
It's also worth mentioning that using a word count tool, such as the one found in most word processors, can help you determine the exact length of your emails. As a general guide, a 50-word email is roughly two short paragraphs, while a 125-word email is about two normal paragraphs plus a short one. Ultimately, the key is to find the right balance between providing enough information to make a compelling case, and not overwhelming the recipient with too much information.