This is one that came up in something I was editing a few days ago. And, I admit, one that I had to check in the dictionary. I was pretty sure the writer wanted unmeasurable (I was right), and I wasn’t sure that immeasurable was a word (I learned something, notably that SpellChecker doesn’t think it’s a word, which is why we still use dictionaries!).
Unmeasurable means, specifically not able to be measured objectively. We use this one in the literal sense: “the immense lizard was unmeasurable with the tiny ruler in the standard lizard measuring kit”; “the sea trench in which the angler fish lived was of an unmeasurable depth”.
Immeasurable means, a bit less specifically, I suppose, too large, extensive or extreme to measure. We should reserve this one for the more figurative sense (otherwise there’s no point in having two different words, is there, and where would THAT leave us?): ” the immeasurable mercy of their god”; “he had immeasurable ambition”.
“I experienced immeasurable relief when I discovered that the width of the lake, filling and evaporating as it did, was actually unmeasurable.”
You can find more troublesome pairs here and the index to them all so far is here.
LibroEditing proofreading, editing, transcription, localisation 
Nordie
August 24, 2012 at 5:15 pm
“The immeasurable depths of space”…..Unmeasurable doesnt sound quite the same does it?
I always imagine unmeasurable to be those things smaller than a universe, but impractical or impossible to quantify a measure.
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Liz at Libro
August 24, 2012 at 5:15 pm
I’d say that was a fair assessment!
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Marlene
December 16, 2014 at 5:04 pm
This info has been unmeasurably
helpful!!! ThankU!!!
ThankU Google for showing this option when I was seeking a definition for immeasurable!!!
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Liz Dexter
December 17, 2014 at 6:40 am
Good use of the word in the comment – congratulations! And I’m glad I could help.
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carmelite
May 29, 2016 at 7:23 pm
Marlene, unless I did not understand the above explanation, you mean “immeasurable”. Information are not something you can measure literally, therefore we are in a figurative context.
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Ada Chen
March 29, 2015 at 6:06 pm
Thank you, I was in fact writing an essay and these definitions really help me out a lot!!
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Grainne
June 19, 2015 at 7:36 pm
I had the opposite reaction. I googled both words because I have always used the word immeasurable in the descriptive context not in the literal context, however on several occasions of late I have seen the word unmeasurable used to describe heartache etc. I was beginning to think I was wrong. Thank you for clarifying.
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Liz Dexter
June 19, 2015 at 7:41 pm
You’re welcome – glad I could help!
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stroudos (@stroudos)
June 24, 2015 at 1:44 pm
I love this comment:
“otherwise there’s no point in having two different words, is there, and where would THAT leave us?”
Sends a shiver up the spine just thinking about it, doesn’t it?
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Sumathi Prasad
July 6, 2016 at 7:52 am
Wow👍Thank you for making me understand more clearly the difference between unmeasurable and immeasurable !!! Somehow I got the feeling that one of the two words didn’t exist?? So I had no choice but Google 😊😊
Looking forward to more insight on the English Language from you…
All the best 👍👍
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Mehrbano Khattak
August 10, 2016 at 8:51 am
maybe if the word is written as “un-measurable”
I had an urge to use this word today and came across your blog
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Liz Dexter
August 10, 2016 at 2:47 pm
Yes, but unfortunately most of the time it’s not written with a hyphen. I’m glad I was able to help anyway.
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Sergio
June 26, 2019 at 4:19 pm
So almost 3 years later and there’s still uncertainty around these 2 words. I was just looking them up and not only is there conflicting info, I’m still wondering why both words seem to only refer to excessive size, whether figuratively or literally. Even in Liz’s examples, both refer to immensity. All this started because I was writing and needed a word to describe something that is so tiny that it cannot be measured. Incalculable, incomputable, un or immeasurable, etc., all point to indefinitely large. If I said, “your market share is unmeasurable”, would you immediately know if I meant too big or too small to measure?
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Liz Dexter
June 26, 2019 at 4:20 pm
Interesting – you’d have to say “unmeasurably tiny” I feel, to make it clear. Good point!
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Sergio
June 27, 2019 at 6:40 pm
Thanks Liz! That’s what I thought too.
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Niels Petter Liset
February 10, 2021 at 1:21 pm
I was thinking about this exact point, and my reflections seem to be close to yours. But I also thought about the words “imperceptible” and “imperceivable” as possible synonyms. Even though these words are related to sensing and perceiving, not measuring, these words are used for something too small to be detectable, and, at least in my context, I was able to use them as synonyms.
Thank you both for the posts!
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