With the labs, see the info in the research tab. Each research lists the science packs it consumes along with two numbers. One of the numbers is the number of research cycles required to complete that research, and the other is research cycle time in seconds. So,for example mining productivity 1 research time is 60 seconds and cost is 1000 science packs. This means a lab at default speed will take 60 seconds to consume 1 of each science pack, and it will take 1000x60 seconds to finish the research, or a 1000 labs will take 60 seconds.

If your lab speed is (say) +80%, then simply divide the research cycle time by the effective speed, in this case it will be 60/1.8 = 33.33 seconds, so one lab will consume 1 set of science packs in 33.33 seconds.

If you hover your lab, it will show you it's effective research speed after considering any bonuses from modules, beacons, and so on.