The Spaulding Readability Formula, developed by Seth Spaulding in 1956, is the first readability formula to score Spanish texts. The formula is:

In this equation:

• D represents the difficulty of the text.
• L is the average sentence length.
• R is the density of rare words.

Rare words are words not found in a list of 1500 frequent lemmas in Spanish, as compiled by Milton Buchanan. Also, rare words exclude words repeated more than twice, days of the week, months, proper names, diminutives and augmentatives of listed words, as well as place names and demonyms.

• Instead of Milton Buchanan's outdated word list, SpanishReadability.com uses a modern word list (updated 2023) of common lemmas in Spanish.

Match the score to the following Spaulding reading scale:

Result	Difficulty (Spaulding)
0-40	First teachings and simplified texts
40-60	Very easy
61-80	Easy
81-100	Slightly difficult
101-120	Difficult
121 or more	Very difficult

We use an updated table to align the score with both a reading scale and grade level.

Score	Reading Level	U.S. Grade	ESP. Grade	Age Group
0-20	Extremely Easy	2nd - 3rd grade	2º - 3º Primaria	7-9 year olds
21-40	Very Easy	4th - 5th grade	4º - 5º Primaria	9-11 year olds
41-60	Easy	6th - 7th grade	6º Primaria - 1º ESO	11-13 year olds
61-80	Average	8th grade	2º ESO	13-14 year olds
81-100	Slightly Difficult	9th - 10th grade	3º - 4º ESO	14-16 year olds
101-120	Difficult	11th - 12th grade	1º - 2º Bachillerato	16-18 year olds
121-140	Very Difficult	College	Universidad	18+ year olds
141+	Extremely Difficult	College Graduate	Postgrado Universitario	20+ year olds