[AllyCat]

If I use a voltage+current measurement device with a solar cell, can I just easily find the W/m2 by multiplying the current with the voltage without needing to find Isc?

Hi and welcome to the forum.

What type of "voltage+current measurement device" do you plan to use?    A normal "wattmeter" needs to be used in association with a suitable load (resistance) and selecting / controlling that is the "difficult" part of solar panel optimisation and management.

But with a simple multimeter you could measure the "Open Circuit voltage" on its Volts range and the "Short Circuit current" (of a SMALL solar cell) on the Amps range.  Multiply those and you might get "somewhere near to" (but more than) the maximum power the cell / panel might be able to produce.  Then you need to take into account the probable energy conversion efficiency of the cell (typically 10% - 20%) and its active area to estimate the solar watts/m².

What type of "Solar Cell" do you have in mind?  Both the low cost "Epoxy coated" and the "Amorphous Silicon" types have various (long-term) accuracy issues.

Cheers,  Alan.