Calculator
Water Filter Calculator
A filter’s box gives you two limits — a gallon capacity and a time limit — and the real answer is whichever one you hit first. This calculator does that math from your own household’s water use and your filter’s own printed numbers.
Published
- Capacity-based interval
- about 58 days
- Recommended replacement interval
- about 58 days
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How we calculate this
- Daily water use (default)
- CDC survey data puts average plain water intake at 44 ounces a day per US adult (2015-2018) — plain water specifically, not coffee, tea, or water in food, which is a reasonable proxy for water that actually passes through a drinking-water filter. The gallons-per-day field is what actually drives the capacity-based estimate, so adjust it if your household also filters water for cooking, pets, or anything beyond drinking. CDC, "Fast Facts: Data on Water Consumption".
- Filter capacity and manufacturer max interval
- Both vary by product and are printed on your filter's own box or NSF certification listing, so there's no figure we could source that would be accurate for your filter — enter your product's own numbers.
- Recommended interval = whichever comes first
- We take the shorter of the capacity-based estimate (how long your stated household use would take to filter the stated capacity) and the manufacturer's own stated max interval — the same "whichever comes first" logic manufacturers themselves use, since a filter can hit its gallon capacity well before its time limit, or vice versa for a low-use household.
Frequently asked questions
- Why two different numbers — capacity-based and recommended?
- The capacity-based interval is pure math: your filter's stated gallon capacity divided by how much water you actually filter per day. The recommended interval also checks that against the manufacturer's stated time limit and uses whichever is shorter, since filter media can degrade with age even if you haven't filtered its full rated capacity yet.
- Where do I find my filter's capacity and max interval?
- Both are typically printed on the box, and NSF-certified filters list capacity in their NSF certification record. If your filter only states one of the two, set the other conservatively (a lower capacity, or a shorter max interval) so the result stays a safe estimate.
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