Free calculator · same math as the app
Water meter usage calculator
Enter meter readings with their dates to get the water used between readings and your average use per day, even with missed days, weekends and a meter reset in the middle.
For use per connection per day
Tick Reset when the meter was reset, replaced or rolled over before that reading. It starts a new baseline, as in the app.
Showing an example: a small park's source meter over nine days.
Paste readings from a spreadsheet
Average 6,171 gal/daySee results
over 8 days in 6 intervals
Hover or tab to a bar for its interval.
| Date | Reading | Days | Usage | Per day |
|---|---|---|---|---|
| Sep 1 07:40 | 1,284,310 | — | First reading — no usage yet | — |
| Sep 2 07:35 | 1,290,020 | 1 | 5,710 | 5,730 |
| Sep 3 07:50 | 1,295,655 | 1 | 5,635 | 5,577 |
| Sep 4 07:45 | 1,301,480 | 1 | 5,825 | 5,845 |
| Sep 7 08:10 | 1,319,300 | 3 | 17,820 | 5,906 |
| Sep 8 07:40 | 1,327,950 | 1 | 8,650 | 8,834 |
| Sep 9 07:45 | 1,333,700 | 1 | 5,750 | 5,730 |
How to calculate water usage from meter readings
A totalizing meter only ever counts up, so the water used between two readings is simply the later reading minus the earlier one. Average use per day is that amount divided by the days between the readings. From the example above:
| Reading | Register | Used since previous | Days | Per day |
|---|---|---|---|---|
| Thu Sep 4, 7:45 | 1,301,480 | — | — | — |
| Mon Sep 7, 8:10 | 1,319,300 | 1,319,300 − 1,301,480 = 17,820 gal | 3 | 17,820 ÷ 3 = 5,940 gal |
Counting the times too, that interval is 3 days and 25 minutes, so the calculator shows about 5,906 gallons per day. Reading at about the same time every day keeps each interval close to 24 hours, so daily figures compare fairly.
Keep the readings, not the differences
It's tempting to log “gallons used today” instead of the register reading. Don't. The register reading can always be checked against the meter and recalculated. A daily difference can't, and one mistake carries into every figure after it. The Water System Logbook app follows the same rule: it stores readings exactly as entered and works out usage whenever it's displayed or exported, never storing it.
When the new reading is lower
A lower reading means one of three things: a misread or transposed digit, a meter that was reset or replaced, or a register that rolled over past its highest number. This calculator, like the app, doesn't guess which. Fix the typo, or tick Reset on that reading so it becomes a new baseline. If you know the register rolled over, the rollover guide shows how to work out the water used across the rollover.
Units, multipliers and conversions
- Multipliers. A register marked “×10” or “×100” counts in tens or hundreds. Multiply the reading before entering it, or enter it as shown and multiply the result.
- Cubic feet. One cubic foot is 7.48 US gallons, so 1,000 ft³ is about 7,480 gallons.
- Cubic meters. One cubic meter is 1,000 liters, or about 264.2 US gallons.
Not sure which dials to read? See how to read a water meter.
Using per-connection figures
For a park or small community, use per connection per day to compare against your own history. Use varies widely with occupancy, season and irrigation, so your baseline matters more than any national number. For a sense of scale, EPA WaterSense puts the average American family at more than 300 gallons a day at home. A sustained jump above your baseline, especially overnight when little water should be used, is the classic sign of a leak. Comparing the source meter with your master or customer meters can confirm it: see the water loss calculator.
Questions
How do I calculate water usage from two meter readings?
Subtract the earlier reading from the later one. That's the water used between them, in the meter's unit. Divide by the number of days between the readings for average use per day. Apply the register's multiplier first if it has one (×10, ×100).
What if I missed a day or skipped the weekend?
Nothing is lost. The next reading covers the whole gap, and the calculator divides by the actual days between readings, so a three-day weekend interval shows the same per-day rate as three single days would.
Why does a reading show as lower than the previous one?
Either a digit was misread or mistyped, or the meter was reset, replaced or rolled over. Correct the typo, or tick Reset for that reading. The calculator then treats it as a new baseline and measures the next interval from it.
Does it work for a pump hour meter?
Yes. Choose Hours as the unit to get run hours per day. To combine pump hours with the source meter and get gallons per minute, use the well pump GPM calculator.
Are my readings saved or sent anywhere?
No. The calculation runs in your browser and nothing is sent to a server. Readings are cleared when you close the page, so download the CSV if you want to keep them.
Sources
Last reviewed September 28, 2026. Rules change and states add their own; confirm with your state drinking water program.