Lumen-per-watt efficiency varies wildly by the quality of the LED. It also varies by the current through the LED - LEDs are more efficient at lower current, and less efficient when driven near their thermal maximums.
The data sheet for the LED strip will plainly state the lumens per segment at any given voltage. It will also state the current per segment at any given voltage. You can multiply current x voltage to get watts at that voltage, and then look up lumens at that voltage and compare.
These types of "LED strip" are rated by voltage (rather than current as a raw LED would be) because they are actually "segments" of 3-6 LEDs in series with a resistor. LEDs have a very steep current/voltage curve, so small changes in voltage has big changes in current, and thus power, and thus lumens. The resistor dampens this somewhat, so the changes are not so extreme. Generally, LED strips are sized so that on automotive battery float voltage with charging system operating (14 or 28 volts), the LED's power is limited to that which will be safe without an added heat-sink. LED strips are generally not used with heat sinks.
The cheapest LED strips may not have spec sheets, because they are opportunistically using whichever LEDs nobody else wants to buy, so the spec changes every batch. In which case you're on your own!