What size custom logo photo is needed to fill the entire square of the basic store logo box?

[auntiejosattic]

I have tried uploading stock pics and clip art in the Display Settings custom logo , and none will completely fill the square logo box, for a basic store.  I can't find any info on how to resize a photo to fit the entire box.

If you know please let me know.

Thanks!

[orangehound]

The two I use are 150x150 (square one) and 1200 wide by 270 tall (banner).