Quantification vs Measurement

Quantification vs Measurement

“If you think you know something about a subject, try to put a number on it. If you can, then maybe you know something about the subject. If you cannot then perhaps you should admit to yourself that your knowledge is of a meager and unsatisfactory kind.”

~ Lord Kelvin, 1893

Some folks seem to mix up the idea of quantification with the idea of measurement.

“Why does it matter?” I suspect you might ask. I’ll leave you to be the arbiter of that.

I just wanted to flag that in my view (and in the dictionary), there’s a difference:


“A fundamental, generic term used when referring to the measurement (count, amount) of a scalar, vector, number of items or to some other way of denominating the value of a collection or group of items.”


“The act of assigning a quantity to (something).”

Tom Gilb defines quantification thusly:

“Quantification, even without subsequent measurement, is a useful aid to clear thinking (what is this about?) and good communication (this is the goal, gang).”

~ Tom Gilb


“To ascertain the quantity of a unit of material via calculated comparison with respect to a standard.”

In A Nutshell

In a nutshell, the two terms differ in that:

  • Quantification is about a way to have more meaningful discussions, less obscured by subjective language, whilst
  • Measurement is about seeing more objectively what’s happening in your world.

In general we can fairly quantify anything; measuring things is often more problematic.

If you have your own definitions which you prefer more, or any other feedback, I’d love to hear from you.

– Bob

Further Reading

Principles of Software Engineering Management ~ Tom Gilb
Competitive Engineering ~ Tom Gilb
Software Metrics ~ Norman E. Fenton
Quantifying Stakeholder Values ~ Tom Gilb (pdf)
Making Metrics More Practical in Systems Engineering ~ Tom Gilb (pdf)

  1. I’ve often found that team shrugs back when I suggest that we measure how our workflow, to know where we are in order to improve. Mind you (and the team) that this is for the team only. Just for us to improve on.

    My guess is that previous measurements in many cases has been used to punish the team instead of helping them. Or that they have been followed up on numbers / goals that they haven’t been part of deciding and setting up for them.

    Do you think that a change in language (talking about Quantification instead of Measurements for example) could change that perceived attitude.

    (Writing this i realize that you will probably ask me why I enforce that on the team. And I don’t. I’ve merely suggested it but every time I’m met with a NO!-attitude. And then we don’t. But I think that data driven decision making could greatly improve the quality of our improvement efforts. )

    • Hi Marcus,

      Can I ask a question?: How do folks in the team feel about the current quality of improvement efforts?

      – Bob

      • I knew you would come back with a question. Thank you for challenging me.

        I think that they don’t think much about the improvement work going on there right now. It’s really not structured at all (no retros, no improvement of board or process otherwhere). My idea was that measuring would create a knowledge on where we stand, as well as show how any improvement work done will improve on the gather measurements.

        So, back to the question related to this post, have you seen this in other teams? Do you think that it’s a intent-thing that can be improved by using other words for it?

  2. I agree that both quantification and measurement can be extremely helpful. It’s also useful to have the distinction between them pointed out. Just a couple of things though:

    “Quantification is about a way to have more meaningful discussions, less obscured by subjective language” – are we saying that subjective language only serves to obscure things? Subjective language is not meaningful? Subjective language is less meaningful than something quantified? Or – perhaps most misleading of all – if something has been quantified, it is not subjective? I wouldn’t agree with any of those propositions.

    As regards Lord Kelvin’s saying: you’ve quoted the paraphrase of this that Tom Gilb made in “Competitive Engineering”. Although Tom did use the verbatim quotation in (the wonderful) “Principles of Software Engineering Management”, he left out the all-important preceding sentence. What Lord Kelvin actually said was:

    “In physical science a first essential step in the direction of learning any subject is to find principles of numerical reckoning and practicable methods for measuring some quality connected with it. I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of science, whatever the matter may be.”

    In other words, he was making a point about methodology specifically in his own discipline – physics. Although, as you’ve shown elsewhere, there’s a lot to be learned from trying to apply scientific method in the context of human and social activity, it isn’t universally applicable. For example, is it valid to say that person A likes something 2.3 times better than person B does?

    • Hey Nick,

      I thank you for your comment, but have to admit to feeling piqued by it. How should I interpret the intent behind your statement about the Lord Kelvin quote? My pique emanates from a feeling of being lectured to – and this does not meet my need for a meaningful connection, nor for mutual learning.

      However, I shall attempt to respond, and hopefully we can find a place where we can learn together about this topic?

      I believe a lack of quantification makes discussion more difficult through increased and unintended ambiguity, when attempting to come to a common understanding of e.g. a requirement. I also believe that joint or mutual quantification of significant aspects or dimensions of e.g. a requirement can help overcome this. I chose to use the terms subjectivity and objectivity to represent this spectrum, but I invite you to rephrase the sentence in question if you feel this was a poor choice of terms.

      And yes, I believe it is valid to say that “person A likes something 2.3 times better than person B” – but only if we can define the term “likes” adequately (see e.g. Gilb on quantifying love).

      – Bob

  3. Toni said:

    I agree that quantifying is not the same as measuring. But to be honest, I do not yet see the point of quantifying something without being able to measure it. Let me try to explain.

    It’s true that ambiguity often arises from the fact that different people interpret differently. That’s why good definitions are crucial. An objective description is therefore something to aim for. Objective in this sense that everyone person understands it in the same way, without need for (subjective) interpretation. Quantification, then, may be ultimate goal as it enables one to put a number to the thing we’re trying to define (see, e.g. Porter).

    If the quantified object can not be measured, however, can one still call the definition objective? If other people can not reproduce the quantification/measurement, then we may still be speaking a different language based on interpretation.

    Please let me know if there is something I misunderstood or misinterpreted in your post.

    Amazon link to Porter: http://www.amazon.com/Trust-Numbers-Theodore-M-Porter/dp/0691029083

    PS: I tried to find Gilb’s take on quantifying love, but without luck. Do you happen to have a reference handy?

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