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DB to DBm conversion

This topic contains 18 replies, has 1 voice, and was last updated by  vadly 5 months, 4 weeks ago.

Viewing 15 posts - 1 through 15 (of 19 total)
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  • #68076 Reply


    hi all

    how can to convert from DB to DBm
    is the formula that DBm=DB+30
    and DB=DBm-30

    #68077 Reply



    no, that is very very wrong.
    dB cannot be converted in dBm ! those are not counting the same thing.

    dBm is an absolute power. It can be converted in Watts.
    2W = 33dBm

    dB is a difference of dBm, and it has no physical existence other than this. It is a mathematical tool.

    For example, from 39dBm to 42dBm, there is a difference of +3 dB.
    You cannot convert 3dB to watts. But you can convert dBm into watts.
    39dBm = 8W
    42dBm = 16W

    but 3dB is not equal to 8W !!!


    #68078 Reply


    thanks pix for explanation , what is the mathematic formula to convert from DBm to Watt and vice versa

    #68079 Reply



    wikipedia, google, etc…


    #68080 Reply


    x = 10 log_{10}(1000P)
    where P is the power in W and x is the power ratio in dBm

    #68081 Reply

    lakhindar murmu

    hi all
    can anybody help me how to visualize group delay response of a microstrip filter in IE3D software?

    #68082 Reply

    Dhananchezhiya Parasuram

    I am using Selective Level Meter(SLM) to measure power line carrier communication gain in this meter its showing only the unit of dBm but I need to measure inform of dB Its there any formula to convert dBm to dB, any one can explain details please.

    #68083 Reply



    dB is not a “measurement” unit, it is a “comparison” unit. Your “dBm” measurement can be converted into mW, W or whatever power unit you want.

    1dB does not mean anything by itself. You can only use “dB” to compare two values. For example: value A is 1dB higher than value B, whatever the values A and B.

    If someone asks you to provide a measurement in “dB”, it means they made a common mistake. They actually want “dBm”.


    #68084 Reply


    As Pix has already stated, but put more simply:

    dBm = an “absolute” measurement of power

    dB = is a “relative” measurement often used to illustrate a value between e.g. two absolute measurements e.g.

    …….> = 3dB relative/difference

    #68085 Reply


    When you are using a Selective Level Meter your are making measurements in a physical circuit, right?, then all the time you are measuring dBm, as the previous answers dB is a relative measure used frequently because you can’t have power directly from that measurements and is more easy to get dB, but in circuits you have power in all parts, then for example to obtain dBs you only need to set a reference.
    For example you measure the input to an specific circuit then you measure the output in both cases you get dBm but you need to say about the gain or loss of your circuit then you make the simple math:
    dB= dBm at output – dBm at input
    From that specific equation if you have a positive dB then you surely have an amplifier and if you have negative dB you have a loss like a network of resistors, if you do the subtraction in opposite way then the signs and interpretations change. I hope this can help you, best regards,

    #68086 Reply

    soe min aung

    How to calculate Microwave linkbuget for a hop?

    #68087 Reply


    30dbm to db

    #68088 Reply


    hi, you cannot convert db to dbm, those are not the same kind of unit at all (like converting WATT to KILOGRAM)

    #68089 Reply


    Perform the following conversions plz:
    i). -15dB to dBm
    ii). -25dBm to mW.
    iii). 1W to dB
    iv). 1W to dBm.

    #68090 Reply


    The information provided for relation between dBm and dB is helpful.Can you please provide the more information for it in case of amplifier electronics??

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