There isn't anything like that. The reason for that is because your mixer doesn't output sound. It outputs electrical signals. Those signals are converted to sound by the speakers and only sound can be measured in SPL.

Here's an example why. Lets say you have a mixer. The outputs of that mixer go to a power amp. The outputs of the power amp go to the speakers. Now lets also say you are using a 50watt power amp. So you play music through the mixer and crank it all the way up as loud as it will go. Your speakers will play the music using whatever signal the 50 watt amp is delivering.
NOW, say you replace that 50 watt amp with a 400 watt amp. Using the same mixer, and speakers and volume settings on the mixer, the audio coming out of the speakers will be much louder resulting in an increase in the SPL level. Nothing on the mixer changed, so there is no way for it to know that the SPL was increased.

So you see there can't be a built in SPL meter in a mixer that doesn't use a microphone to actually measure the "sound pressure"

Go to Radio Shack and buy one or you can get an SPL meter at Sam Ash or GC.

hmmm, i dont think there's a radio shack in pakistan? :wink:

But they are online. And they have reissued their analog Spl meter, which I have heard is preferable to the digital version.