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Convert lb/mmBTU to kg/GJ

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  • Convert lb/mmBTU to kg/GJ

    I am needing someone to fact check this so I am not being stupid and overlooking something.

    The conversion of BTU to J is 1 to 1055.05585262
    And thus, 1 mmBTU is 1055055852.62 J
    And thus, 1 mmBTU is 1.05505585262 GJ
    The conversion of lb to kg is 0.453592370

    Taking 1.05505565262 times 0.453592370 I get 0.478565285 which would be a conversion factor for lb/mmBTU to kg/GJ
    Thus, 0.218 lb/mmBTU equals 0.104 kg/GJ


    And of course factoring in any exponent of gram or Joule that I want at this point.


    Am I wrong, and where am I wrong?

  • #2
    Originally posted by HK57 View Post
    I am needing someone to fact check this so I am not being stupid and overlooking something.

    The conversion of BTU to J is 1 to 1055.05585262
    And thus, 1 mmBTU is 1055055852.62 J
    And thus, 1 mmBTU is 1.05505585262 GJ
    The conversion of lb to kg is 0.453592370

    Taking 1.05505565262 times 0.453592370 I get 0.478565285 which would be a conversion factor for lb/mmBTU to kg/GJ
    Thus, 0.218 lb/mmBTU equals 0.104 kg/GJ


    And of course factoring in any exponent of gram or Joule that I want at this point.


    Am I wrong, and where am I wrong?
    You are close but you multiplied by one conversion when you should have divided; easy mistake when converting a complicated number with multiple units in numerator and denominator.

    In that case, I strongly recommend that you always write out the problem WITH units and use the principle of unit cancellation to make sure you are getting what you intended. Each of your individual conversions is correct and a conversion like 1 lb = 0.453 592 37 kg can also be written as 1 = 0.453 592 37 kg/1 lb. You can always multiply or divide by 1 without changing anything. Should you multiply or divide? You do the one that cancels the unwanted unit and leaves the wanted unit:

    0.218 lb/MMBTU x 0.453 592 37 kg/1 lb x 1MMBTU/1.05505585262 GJ = 0.0978 kg/GJ

    Of course, your calculator doesn't know about units, it just does arithmetic with numbers, but If you set the problem up like this you are much less likely to perform the wrong operation. You likely learned this in school, but most people HATE showing their work with numbers. However, it avoids a lot of errors.

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    • #3
      Thank you.

      I am understanding what you are doing differently:
      0.453 592 37 x 1.055 055 652 62 = 0.478 565 285 is wrong; it should be
      0.453 592 37 / 1.055 055 652 62 = 0.429 922 614 as the conversion ratio.

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