Maximizing S-Corp Employer contribution to 401(k)

[inddan]

I am the sole owner/employee of an S-Corp. I have already contributed the maximum employee 401k contribution and also want to have the S-Corp contribute the maximum Employer contribution to my 401(k). I understand the maximum limit for employer contributions is 25% of my W2 salary. But should I use W2 box 1 (wages) or box 3 (Social Security wages) for that calculation? Is it legal to use box 3 since it is higher than box 1 and will allow the S-Corp to contribute more to my 401(k)?

Thanks for your help!

[Critter]

Actually you use the GROSS pay amount which is usually the amount in box 5 on the W-2  not boxes 1 or 3.