How to use
- Measure or estimate the actual amount placed in the bath and select litres or US gallons.
- Enter the shower’s measured flow per minute, the minutes for one shower, and how many showers to compare.
- Select Compare water use to see both totals and the absolute difference.
- Edit any value to discard the old comparison; Clear removes numbers and keeps unit choices.
Formula
Shower water = flow per minute × minutes per shower × number of showers. Bath water is the amount you enter.
Both totals are converted internally to litres before comparison. One US gallon equals 3.785411784 litres.
Examples
One bath and one shower
A 100 L bath compared with 8 L/min for 10 minutes gives 100 L versus 80 L; the shower uses 20 L less.
Several showers
At 2 US gal/min for 8 minutes, two showers use 32 US gal. Compare that measured total with your own bath fill.
Limits
- The calculator does not assume a flow rate for a showerhead type. Measure with a container and timer when accuracy matters.
- It compares water volume only, not heating energy, cost, comfort, hygiene, or health outcomes.
- Bath fill levels and shower flow can change between uses; the result is only as representative as the inputs.
- US gallons are used; Imperial gallons are not supported on this page.
Frequently asked questions
How can I measure shower flow?
Collect water for a known number of seconds, convert that amount to one minute, and enter the measured rate.
Does a shower always use less?
No. The result depends on your actual flow rate, duration, count, and bath volume.
Does the bath volume mean tub capacity?
Enter the water actually used, not the maximum manufacturer capacity unless you fill it completely.
Can I compare more than one shower?
Yes. Use the whole-number shower count field.