# Converting -10dbm to dbu?

I know that -10dbm is supposed to be lesser than 4dbu. But somehow, the online converter I used to convert dbm to dbu showed the former to be 40dbu, which I believe cannot be the case. So, here's the question.

How to convert the following specs to a definite dbu?

• Rated output level: -10dbm
• Output load impedance: 10kΩ or more

Edit: Adding more information. I am connecting the zoom h1 (with above specs) to a behringer mixer line input, which says impedance: min 4.7kohm.

• Did you get an answer of 40dBu or 40dBuV? – Timinycricket Sep 26 '18 at 20:05
• @Timinycricket 40dBuA & 120dBuV – Srikanth Sep 26 '18 at 21:33
• the uV stands for microvolts and would mean 40dBuV is -85dBu. I think your specs were supposed to say -10dbV because that is consumer line level. It might be a typo when it says dBm – Timinycricket Sep 26 '18 at 22:14
• Just verified. Looks like zoom alternates between dbv & dbm in many models. – Srikanth Sep 26 '18 at 23:53

First convert `dbm` to `Watts` using the following:

``````Pw = 10^(Pdbm/10) / 1000

Pw = 10^(-10/10) / 1000 = 0.0001 Watts
``````

So the max output power is 0.0001 Watts, and the output load impedance is 10 kOhm. We can now use Ohm's Law to calculate the Voltage:

``````V = I * R
P = I * V
``````

which makes

``````V = SQRT(P * R)

V = SQRT(0.0001 * 10000) = 1 Volt
``````

now you can go from Volt to dbuV

``````Vdbu = 20log(V/0.775)

Vdbu = 20log(1/0.775) = +2.2 dbuV
``````

HTH