THE NUMORIX GUIDE
How to use the Water Usage Calculator
Last reviewed September 14, 2026
What this calculator does
The engine calculates gallons as flowRate x minutes / 7.
Formula and method
The engine calculates gallons as flowRate x minutes / 7.481 and cost as gallons x rate. It rounds gallons and cost to four decimals. The UI labels flow rate as gallons per minute and rate as dollars per gallon, so the division by 7.481 is part of the implementation and must be included when reproducing the displayed result.
Variables and inputs
Enter flow rate in the UI's gal/min field, duration in minutes, and a water rate in dollars per gallon. The returned values include the original inputs, calculated gallons, and cost. The engine does not ask for a separate sewer rate, fixed charge, fixture type, or meter reading.
Worked example
With a displayed flow rate of 2 gal/min, 10 minutes, and a rate of $0.005/gal, the engine calculates 2 x 10 / 7.481 = 2.6734 gallons. Cost is 2.6734 x $0.005 = $0.0134 after rounding, which is the value shown by the UI.
How to interpret the result
This output is the result of the route's formula, not a direct meter measurement. If the flow field is truly in gallons per minute, a reader might expect 2 x 10 = 20 gallons; the engine's divisor means the displayed number should be treated cautiously.
Common mistakes to avoid
Do not reproduce the result by multiplying the labeled flow rate and minutes alone; include the engine's / 7.481 divisor. Enter rate in dollars per gallon and distinguish a usage rate from a utility bill's fixed or tiered charges.
Assumptions and limitations
The flow-unit label and formula are not internally consistent for a normal gallons-per-minute calculation, and the engine does not document what the 7.481 divisor is intended to represent. It omits pressure, fixture variation, leaks, temperature, sewer charges, tiered pricing, minimum bills, and actual meter rounding. Verify the unit convention before using the cost for conservation or billing decisions.