Those of us who come from the humanities tend to find math formulas a bit complicated (I could even say they’re my personal Vietnam flashbacks…) But have you ever stopped to think if your text is actually understandable, or if you’re the only one who gets it?
It’s a question more people should ask themselves before publishing anything. Because even if we think we’re the next Stephen King, if the reader doesn’t grasp the idea right away… something is definitely off. Luckily, there’s a readability formula (yes, a math one, but relax!) that can help you find out whether your text makes sense or not. And no, it’s not some modern invention: major publishers, teachers, journalists and communication experts have been using it for decades. Its goal is simple: to help you write in a way anyone can understand.
The formula gives you a number. The higher the number, the better. The lower it is, the more you’re getting tangled up. That simple. But don’t worry, we’ll explain it. We’re also humanities people and got it right away!
The readability formula
The readability formula, also known as the reading ease index, is a mathematical tool that evaluates whether a text is easy or difficult to read.
It’s based on two things: the average sentence length and the average word length. The longer and more convoluted both are, the harder it will be to understand what you’re saying. Makes sense, doesn’t it?
Spaulding’s theory
It was in 1956 that Seth Spaulding proposed the first formula, specifically for texts in Spanish, although it works for any language. The formula is:
D = 1.609L + 331.8R + 22
And what does that mean?
- D = difficulty
- L = average sentence length
- R = proportion of rare words
What now?
Okay, the result this equation gives you comes with scales, from “early learning” texts like the books we read in primary school to exceptionally difficult. If your text scores over 120… it’s time for a rewrite because it’s considered especially hard, while texts under 40 are pretty manageable for beginners.
Gutiérrez de Polini:
Spaulding wasn’t the only one to come up with an equation. Luisa Elena Gutiérrez de Polini also created her own formula based on comprehensibility (C):
C = 95.2 – 9.7L – 0.35P
L = total number of letters
P = total number of words
F = number of sentences
In this case, the lower the resulting value, the more difficult the text is considered to be.
Fernández Huerta: the most cited
The Fernández Huerta index is one of the most frequently cited, adapted from the Flesch formula, which is very popular in English. The equation is:
L = 206.84 – 0.60P – 1.02F
Where:
- P is the number of syllables per 100 words
- F is the number of sentences per 100 words
In this case, a high score means your text is easy to read, and a very low score corresponds to academic, legal or scientific texts.
Szigriszt-Pazos: the empirical approach
This doctor came up with the theory of the Perspicuity Formula, which refers to a text’s quality of being clear, legible and understandable. It has a slightly more complex formula:
P = 205.835 – ((62.3S)/p) – (p/F)
- P = Perspicuity
- S = total syllables
- p = number of words
- F = number of sentences
As we said, this equation is a bit more complex and follows the same logic as the previous one: a very low score means the text is very hard.
And believe it or not, there are still more theories about your texts’ readability, but they’re much harder to understand, like the INFLESZ scale or the µ index by Muñoz Baquedano and Muñoz de Urra. And then we complain about writing being hard… it’s not like we lack tools!
Why writing clearly matters
You might think that writing in a complicated way sounds more serious or intelligent. Wrong. Most readers don’t want to complicate their lives. They want to understand what you’re saying, quickly and without effort. Clear writing isn’t simplistic, it’s effective.
How do I improve my texts?
Even though we’ve shown you all these formulas, you don’t need to pull out a calculator every time you write. Here are some tips:
- Short sentences, clear ideas
- Simple vocabulary
- Avoid unnecessary jargon
- Read it out loud, if you run out of breath reading it, your reader will too.