In various publications, the difference between SSB and CW, is given as 13 dB.
The difference in power between CW and WSPR is 13 dB. (Click)
Or somewhere between 15 dB and 11 dB.
So when I take a figure of 13 dB for both values above, I estimate that the
difference between SSB and WSPR is 13 + 13 = 26 dB or 20 x 20 = 400 in power.
So 400 W in SSB can be compared with 1 W in WSPR.
WSPR - CW - SSB
For an advantage of 26 dB, the power in WSPR can be 1/400th of the power in SSB or 1/20th of the power in CW. This means that the power in WSPR, must be much lower, than the power used in SSB.
If you use a speech processor, you can use a lower value than 26 dB. E.g. 22 dB.
So you can use WSPR for a propagation analysis, to see what is possible with your SSB station.
How to use WSPR to see what's possible with SSB
A power of 80 Watts in SSB or 4 W in CW, can be compared with a power of 200 mW in WSPR.
As a CW enthusiast you can use WSPR spots made with 20 mW or 50 mW to analyse with WSPR where your CW signal of 400 mW to 1 Watt can be heard.