Turning meter readings into MGD
A meter’s totalizer only counts up. Reports, permits and pump schedules talk in million gallons a day. This page turns one into the other: the arithmetic, the four places it goes wrong, and a way to check the answer. We worked through every figure here on November 1, 2026, with the same arithmetic ShiftRounds uses.
The short answer
Take two readings, and the hours between them:
Flow in MGD(This reading − the last one) × gallons per count ÷ hours between them × 24 ÷ 1,000,000
- Gallons per count comes from the dial’s marking. A dial in ×1,000 gallons counts 1,000 gallons a count.
- Use the real hours between the readings, not 24.
- A dial that rolled over: count up to its highest reading, one more to zero, then what it reads now.
- A dial in cubic feet: one cubic foot is 7.4805 gallons.
- Gallons a minute: MGD × 694.4.
What one count is worth
A totalizer shows a count, and the dial says what one count is. Read the number the way the dial shows it, then multiply by what one count is worth:
| The dial counts in | Also written | One count is |
|---|---|---|
| Gallons | gal | 1 gallon |
| ×10 gallons | ×10 | 10 gallons |
| ×100 gallons | ×100 | 100 gallons |
| ×1,000 gallons | ×1000, kgal | 1,000 gallons |
| Million gallons | MG | 1,000,000 gallons |
| Cubic feet | cu ft, CF | 7.4805 gallons |
| ×100 cubic feet | CCF, HCF | 748.05 gallons |
- A printed multiplier. A dial marked ×10, ×100 or ×1000 counts in tens, hundreds or thousands of its unit. A reading of 1,033,045 on a dial marked ×1000 gal is 1,033,045,000 gallons.
- Painted zeros. Some dials show zeros after the turning wheels that never move. Read them as part of the number, in gallons, or leave them off and count in thousands. Do it the same way every time.
- The sweep hand. A large hand or a small spinning wheel on the dial is for testing and finding leaks. It isn’t part of the total.
- No marking at all. The meter’s data plate or the maker’s manual gives the unit. A meter that counts cubic feet looks like any other until its flow comes out about seven and a half times too low.
From two readings to MGD
Subtract the last reading from this one to get the counts between them. Multiply by what one count is worth to get gallons. Divide by the hours between the readings to get gallons an hour, and multiply by 24 to get gallons a day. Divide that by 1,000,000 for million gallons a day.
A shift’s flow
The finished water meter counts in ×1,000 gallons. It read 1,033,045 at 6:00 AM and 1,033,488 at 2:00 PM.
Worked through1,033,488 − 1,033,045 is 443 counts, or 443,000 gallons in 8 hours. 443,000 ÷ 8 × 24 is 1,329,000 gallons a day, or 1.33 MGD.
Readings that aren’t 24 hours apart
Dividing the change by 24 assumes the readings were exactly a day apart, and rounds rarely are. A reading taken late makes the day look busier than it was, and one taken early makes it look quieter.
A reading two and a half hours late
The raw water meter counts in million gallons, to three places. It read 1,282.809 at 6:00 AM Monday and 1,284.274 at 8:30 AM Tuesday, 26.5 hours later.
Worked through1,284.274 − 1,282.809 is 1.465 MG. 1.465 ÷ 26.5 × 24 is 1.33 MGD. Divided by 24 instead, it reads 1.47 MGD, 10% high.
For a monthly report, read the meters at the same hour every day. Then the change from one day’s reading to the next is that day’s flow, with nothing to work out but the multiplier.
Readings only minutes apart say more about the clock than the flow: a minute’s error in either time is a large share of a short span.
A dial that rolled over
A totalizer has a fixed number of wheels. After its highest reading, such as 9,999,999, it goes back to zero and keeps counting. The next reading is smaller than the last, and subtracting gives a large negative number. Count it in three steps instead: up to the dial’s highest reading, one more count to reach zero, and then what it reads now.
Counts across a rollover(Highest reading − the last reading) + 1 + this reading
A seven-wheel dial that rolled over overnight
The dial counts in ×1,000 gallons, and its highest reading is 9,999,999. It read 9,999,812 at 10:00 PM and 255 at 6:00 AM.
Worked through9,999,999 − 9,999,812 is 187, one more to zero, and 255 after that: 443 counts, or 443,000 gallons in 8 hours. That’s 1.33 MGD.
On a dial that reads to three places, the one count is 0.001. From 9,999.800 to 0.243 MG is 0.199 + 0.001 + 0.243, or 0.443 MG.
A smaller reading isn’t always a rollover. If the last reading was nowhere near the top of the dial, one of the two readings is wrong, or the register was changed. Check the dial before you use either one.
Meters that count cubic feet
A gallon is 231 cubic inches and a cubic foot is 1,728, so a cubic foot holds 7.4805 gallons. A dial in cubic feet turns into gallons with one more multiplication. A dial in hundreds of cubic feet, written CCF or HCF on a bill, counts 748.05 gallons a count.
A meter in hundreds of cubic feet
A dial counting ×100 cubic feet read 48,210 at 7:00 AM and 49,992 at 7:00 AM the next day.
Worked through49,992 − 48,210 is 1,782 counts. 1,782 × 748.05 is about 1,333,000 gallons in 24 hours, or 1.33 MGD.
Gallons a minute and small flows
A million gallons a day suits a plant. At a lift station or a small system it makes for long decimals, and gallons a minute reads better.
| To turn | Into | Multiply by |
|---|---|---|
| MGD | gallons a minute | 694.4 |
| Gallons a minute | MGD | 0.00144 |
| Gallons a minute | gallons a day | 1,440 |
| MGD | cubic feet a second | 1.547 |
A lift station
The lift station’s meter counts in gallons. It read 4,206,915 at 7:00 AM and 4,225,365 at 2:30 PM.
Worked throughThat’s 18,450 gallons in 7.5 hours, or 2,460 gallons an hour: 59,040 gallons a day, 0.059 MGD, or 41 gallons a minute.
Checking the dial against the flow rate
The totalizer and the flow rate come from the same meter, so they should agree. Over a shift, the average flow rate times the minutes should come close to what the dial counted.
Against SCADA’s average flow
SCADA showed the finished water flow averaging 920 gallons a minute over the 8-hour shift above, while the dial counted 443,000 gallons.
Worked through920 × 60 × 8 is 441,600 gallons, 1,400 short of the dial: 0.3% apart.
A small gap is normal, since SCADA’s average and the dial are measured differently. A gap that grows, or shows up shift after shift, means it’s time to check the meter’s calibration.
Keeping track of it in ShiftRounds
ShiftRounds does this arithmetic on every meter reading. A supervisor sets each meter up once, under Checkpoints, and operators type the digits the way the dial shows them.
- The dial’s unit. “The dial counts in” offers each marking in the table above, plus hours for run time and anything else typed in. Each reading keeps its unit, so a meter’s history still reads right after its dial is changed.
- The flow, as it’s typed. The keypad shows the change since the last reading and the flow it works out to in MGD, from the last reading’s time to now. The round’s report shows the same.
- Readings less than an hour apart show no flow.
- A rollover. With the dial’s highest reading set, a reading lower than the last counts as a rollover when the last one was in the top tenth of the dial. Otherwise it reads “Went backward” in yellow before it’s saved, and the report shows it as a finding.
- The expected change per round. A change outside it is a yellow finding, so a meter that stopped, or a slipped digit, shows on the round.
- SCADA. A meter checked against SCADA asks for SCADA’s totalizer too, and the sign turns yellow when the two are more than 0.5% apart, or whatever difference a supervisor allows.
- Over a month, Trends shows each reading with its flow, and the average: “Averaging 443 ×1,000 gal a round, about 1.33 MGD”.
For the monthly operating report, Export in the console downloads each meter’s daily flow as a spreadsheet: the day’s first reading, the next reading on a later day, the hours between, the change, the million gallons and the MGD, worked out as above, rollovers included. ShiftRounds doesn’t fill in the report itself. The meter checklist shows what a meter checkpoint asks on a round.