Battery chemistry & storage
Enter your module count and dimensions, plus your rack's usable height. Get the number of racks needed and the resulting floor footprint.
How it works
Step 1
Use the module count calculator first if you haven't already settled on how many modules your system needs, and the cell count calculator if you're working from bare cells instead.
Step 2
Pull these from the manufacturer's datasheets rather than estimating, since even small dimension errors compound across a full stack.
Step 3
This tool estimates the rack's own footprint only. Check your specific product's clearance requirements for ventilation and service access before finalizing a layout.
The maximum modules per rack this tool calculates assumes modules stack with no gap, which rarely matches real hardware once you account for mounting brackets, cabling, and vendor-recommended spacing. Treat the calculated figure as an upper bound and leave some margin below it for a real installation, and if the resulting stack height or weight is pushing the limits of the space you have in mind, the structural engineer assessment cost estimator gives a sense of what a professional check would cost before you commit to a layout.
A tall, narrow rack can hold many modules in a small footprint, but once you exceed one rack's capacity, the footprint effectively doubles or triples as additional racks sit side by side. This is why the footprint size comparison and this rack sizing tool can tell different parts of the same space-planning story, and it's also why the clearance rules in NFPA 855, Standard for the Installation of Stationary Energy Storage Systems, matter more as rack count grows, since each additional rack needs its own service access space too.
A rack rated for a certain height of modules may still have a separate structural weight limit that binds first, especially for heavier chemistries. Cross-check your rack's weight rating against the chemistry weight comparison for your specific module count before assuming height is the only constraint, since chemistry packaging density is an area NREL's energy storage research continues to work on, with real weight-per-module figures still varying widely between manufacturers.
Once you know how many racks you need, factor that count into your overall installation footprint alongside the clearance space your specific products require. If you haven't finalized your target capacity yet, the whole home backup sizing calculator is worth running first, since that decision determines the module count this tool starts from.
Questions
A rack with 78 inches of usable height stacking 3.5-inch modules can hold roughly 22 modules, a figure that scales with your specific module height and rack's usable internal height, though real installations often leave some margin rather than filling every possible slot.
Leaving some margin below the theoretical maximum is common practice, both for future expansion and to account for real-world clearances like cabling, ventilation gaps, and mounting hardware that this simplified calculation doesn't capture. Treat the calculated capacity as an upper bound, not a target to hit exactly.
A vertical rack still occupies its own floor footprint based on its width and depth, and adding a second rack beside the first doubles that footprint even though height stays the same. Multiple racks side by side can add up to more floor space than expected for a large module count.
Most manufacturers specify minimum clearance requirements for ventilation, cabling access, and service space around a rack, typically in the range of a foot or more depending on the product. Check your specific rack and battery documentation, since this calculator only estimates the rack's own footprint, not the clearance around it.