Metrics Explained

Understanding the readability metrics and scores used by Claru

What are Readability Metrics ?

We test how hard your original Document is to read. We also test if after Conversion. We use special Tests that look at things like:

  • How long your Sentences are
  • How hard your Words are
  • How many Syllables Words have

We use 5 different Tests. Each Test checks different things. This helps us make sure your Easy Read Document is really easy to read.

Want to Check Your Document's Readability ?

Use our Free Online Readability Checker to test your Document before converting it. Get all 5 Metrics instantly — no sign-up required.

Try Free Readability Checker

Flesch Reading Ease Score

What it does: This Test shows how easy your Text is to read.

How it works: It looks at how long your Sentences are and how many Syllables your Words have.

The Scores: You get a Score from 0 to 100. Higher Scores mean easier to read.

Why we use it: This Test has been used since the 1940s. Governments and Schools use it all over the World.

UK Reading Levels:
  • 90-100 Very Easy (Primary School)
  • 80-89 Easy (Year 6-7 level)
  • 70-79 Fairly Easy (Year 8-9 level)
  • 60-69 Standard (GCSE level)
  • 50-59 Fairly Difficult (A-Level)
  • 30-49 Difficult (University level)
  • 0-29 Very Difficult (Postgraduate level)

Flesch-Kincaid Grade Level (Reading Level)

What it does: This Test tells you what School Year you need to be in to understand the Text.

How it works: It looks at Sentence Length and Syllables to work out Difficulty.

The Scores: Lower School Years mean easier to read.

Why we use it: The US Navy created this Test in the 1970s. We changed it to use UK School Years instead of American Grades.

UK School Year Equivalents:
  • Reception/Year 1: Ages 4-6
  • Years 2-6: Ages 7-11 (Primary)
  • Years 7-9: Ages 12-14 (Secondary)
  • Years 10-11: Ages 15-16 (GCSE)
  • Years 12-13: Ages 17-18 (A-Level)
  • University: Ages 18-22
  • Postgraduate: 22+ years

Dale-Chall Readability Score

What it does: This test looks for hard words that people might not know.

How it works: It has a list of 3,000 easy words that most Year 4 children know. If your text uses words not on this list, they are "difficult" words.

The scores: You get a score from 0 to 10. Lower scores mean easier to read.

Why we use it: This test is better at finding difficult words than just counting syllables. It knows which words people actually find hard.

Score Interpretation:
  • 4.9 or below Year 4 and below
  • 5.0-5.9 Years 5-6
  • 6.0-6.9 Years 7-8
  • 7.0-7.9 Years 9-10
  • 8.0-8.9 Years 11-12
  • 9.0-9.9 Year 13 (Sixth Form)
  • 10.0+ University level

Gunning Fog Index

What it does: This test finds long words and long sentences that make reading hard.

How it works: It counts words with 3 or more syllables. These are "complex" words.

The scores: Lower school year scores mean easier to read.

Why we use it: A newspaper publisher called Robert Gunning made this test in 1952. It is good at finding writing that is harder than it needs to be.

Target Levels:
  • 6-8: Easy to read
  • 9-12: Acceptable for general public
  • 13-16: Difficult - university level
  • 17+: Very difficult - postgraduate
Industry Standards:
• Newspapers: 8-11
• Popular magazines: 10-13
• Government documents: Should be 12 or less

Automated Readability Index (ARI)

What it does: This test counts letters in words instead of syllables.

How it works: It looks at how many letters are in your words and how long your sentences are.

The scores: Lower school year scores mean easier to read.

Why we use it: The US Air Force made this test in 1967. It is faster for computers to use because it counts letters, not syllables.

What makes it different:
  • ✓ Does not count syllables
  • ✓ Works well with technical writing
  • ✓ Works the same in different languages
  • ✓ Easy for computers to use
Note: ARI usually gives easier scores than other tests for the same text.

Why We Use Multiple Metrics

Each test is good at different things:
  • Flesch Reading Ease: Most people know this test
  • Flesch-Kincaid: Tells you the school year needed
  • Dale-Chall: Finds words people do not know
  • Gunning Fog: Finds sentences that are too long
  • ARI: Easy for computers to use
Using all 5 tests together gives us:
  • Better answers
  • We can find different problems
  • We can check our work
  • We know our Easy Read version is better
  • Professional results

Easy Read Target Scores

For good Easy Read documents, Claru tries to get these scores:

Flesch Reading Ease
80 — 100

Easy to Very Easy

School Year Level
Year 6 or below

Age 11 and under

Sentence Length
8 — 12 words

Short and clear