Flash power is at best confusing and difficult to compare on a like for like basis, at worst almost it’s meaningless.

Speedlights are typically quoted as having a particular Guide Number. Guide Numbers indicate the f stop required for a particular distance at a specified ISO;

f = GN / distance

A Nikon SB700 for example is quoted as having a GN of 28 (meters) at ISO100; so the f stop required at 10 meters is 28 / 10 = f2.8

but then there is also the question of light distribution or spread - what angle is that light covering? So to be really meaningful Nikon also has to quote this GN for this ISO using a 35mm lens on a full frame sensor.

So Guide Numbers need a lot of additional information to make them anything like meaningful, but you then still have the problem that different manufacturers quote GNs for different ISOs and different lens focal lengths, making direct comparisons very difficult.

Studio lights tend to be quoted as having a power in watt-seconds. A watt-second is the power required to deliver one watt for one second. One watt-second is the same as one Joule, which is a standard measure of energy. There is a problem with this as a measure for studio lights though because its a measure of power, not a measure of light.

So watt-seconds suffer from being only an indirect measure of the light output from a studio light. In simple power terms a 1,000 ws light is twice as powerful as a 500ws light, so (everything else equal) if you are at f16 with a 1,000ws light you will need f8 with a 500ws light. But … ws is only a measure of the power delivery from the capacitor, not a measure of the amount of light which is actually delivered.

The amount of light which any particular studio flash will actually deliver will also depend upon the efficiency of the rest of the design, and in order to achieve like for like comparisons you also need to eliminate other variables like the spread of light (angle of view / lens focal length etc).

A number of practical examples of what is required in order to get a proper like for like comparison are available on YouTube.

Mark Wallace provides a good explanation at;

https://www.youtube.com/watch?v=E-ro-ST3iuo

Neil van Neikerk compares three Profoto units at

https://neilvn.com/tangents/profoto-b10-review-comparing-power-of-profoto-b10/

If you want to use a direct measure of light then consider Lumen and Lux. Lumen is a measure of light in the spectrum visible by human beings emitted by a source. Lux is one lumen per square meter. Not many flash manufacturers quote lumen or lux and even then for this to be meaningful you still need to consider at what distance it is measured, as light falls off over distance in accordance with the inverse square law - if you double the distance from the flash to the subject you will only get one quarter of the light intensity, because at double the distance the light spreads out to cover twice the height and twice the width, which is four times the area. If you can bear the maths try Mark Wallace again;

https://www.youtube.com/watch?v=nk9cTa3UthM

Good luck then selecting the flash units which best meet your needs. In the real world the relative measures of flash power can only be a guide to how they will actually perform for you.