What this checker catches
Two products can carry similar marketing labels and still fit very different houses. The checker separates service flow from usable softening capacity, then compares each with the target you entered.
Use service flow, not only “peak” flow
A short peak-flow number is not the same as a continuous service-flow rating. If a product publishes only a peak number, treat the hydraulic fit as unverified until you find the service-flow and pressure-drop data.
Use usable capacity, not only the box label
Nominal grain labels do not tell you the usable capacity at every salt dose. Enter the actual usable capacity from the manufacturer’s performance data when possible.
Certification is a separate gate
Passing the sizing checks does not prove contaminant reduction. NSF explains that standards such as 42, 53 and 44 cover different claims and technologies. Verify the exact model and exact claim relevant to your water.