Water treatment · Filters
Water filter cost per gallon.
Price a filter by what it actually treats, whichever limit hits first: rated gallons or months.
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Water Filter Cost per Gallon Calculator: how it works
Cost per gallon = filter price divided by the gallons it treats before you replace it. The gallons treated are the lower of the rated capacity and the water you actually pass through in the replacement interval (months x 30.4375 days x gallons per day). One US gallon is 3.785 litres.
Worked example. A $60 cartridge rated for 1,000 gallons that you replace every 6 months, filtering 3 gallons a day: in 6 months you pass 6 x 30.4375 x 3 = 548 gallons, below the 1,000 rating, so time is the limit. Cost is $60 / 547.9 = $0.1095 per gallon ($0.0289 per litre), about 2.0 filters and $119.92 a year. A $40 filter rated 500 gallons with no time limit is $0.08 per gallon.
Use the maker's numbers. Rated capacity and replacement time come from the filter's own packaging or datasheet. This is price arithmetic only; it says nothing about what a filter removes. Check certification for the contaminants you care about.
Frequently asked questions
How do I work out filter cost per gallon?
Divide the filter price by the gallons it treats before replacement. $60 over 547.9 gallons is about $0.11 per gallon.
What if I replace on time, not capacity?
Enter the months and your daily use. The calculator uses whichever limit is reached first.
Why is my per-gallon cost higher than the rated figure?
If you use less water than the rating assumes, the time limit hits first and each gallon carries more of the price.
Does this tell me if a filter is any good?
No. It only compares cost. Check the filter certification for the contaminants you want removed.
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Checked
This tool is arithmetic on the numbers you enter. The constants used are 1 US gallon = 3.785 litres and 30.4375 days per month (365.25 / 12), plus 365 days per year for the annual figures.
Runs entirely in your browser. Nothing you type is sent or stored.
Not professional advice
Cost arithmetic only. Not a statement about filter performance or water safety. Not professional advice.