No. Unfortunately not. It can be wildly different strengths. Hopefully it lists the IMCU on the package. For liquid rennet, "single strength" is 200 IMCU per ml (or 1000 IMCU per tsp). I hope I don't get this wrong... I'm actuall *in bed* as I type this.... 1000 IMCU corresponds to the amount needed to coagulating 25 liters of milk. The most popular non-animal rennet tablets I know of are Fromase 50 tablets that are rated at 2305 IMCU per tablet and coagulates 50 liters of milk. You will notice that this is slightly more IMCU power per liter of milk than the standard calls for. I think the standard works well for raw milk and I agree with Fromase's levels for pasteurised milk (or at least, this amount lets me hit my timings almost exactly).
If you see recipes that call for 1/4 tsp of single strength rennet, you can assume 250 IMCU. Normally that's for 1 US gallon of milk which is 3.785 liters, or ~66 IMCU per liter. Fromase's recommendation calles for 46 IMCU per liter and the standard calls for 40 IMCU per liter -- so you can see that most recipes over rennet.
Hope that helps!