How To Measure UPS LOAD

Is there a site that anyone knows of that has detailed info regarding UPS aside from apc?

We are looking at expanding our UPS and Gensat but until now we had our colo company handle everything. With our new Building about to be lite we are still sourcing out our UPS and Gensat.

Total Built space is 2900 square feet with 4x 15 ton 4 step Lieberts.

we have total power of 800amp 3phase and would like to ensure from start we have enough to handle full load.

We have seen in past with colo company that over time they had to increase the size of ups during the years and this has caused downtime for clients. We want to ensure from get go that there is no power issues down the road so rather invest the money now to ensure we can manage a full load down the road.