Bath vs Shower Water Calculator
Compare water used by a bath versus a shower.
About the Bath vs Shower Water Calculator
Compares the water used by filling a bath against taking a shower of a given length, so you can see which uses less.
$$ shower = flow \times minutes $$
How to use
Enter bath volume, shower flow rate and shower duration, then click Calculate.
Worked example
A 120 L bath vs a 9 L/min shower for 8 min (72 L) → the shower saves 48 L.
How to use this calculator
- Enter the bath fill rate and bath time.
- Enter the shower flow rate and shower time.
- Compare the two totals to see which uses more water.
- If needed, review the difference to understand the savings.
The formula explained
$$ \text{bath water used} = \text{bath fill rate} \times \text{bath time} and \text{shower water used} = \text{shower flow rate} \times \text{shower time} $$
- \(\text{bath fill rate}\) = How many liters or gallons the bath uses per minute while filling
- \(\text{bath time}\) = How long the bath runs in minutes
- \(\text{shower flow rate}\) = How many liters or gallons the shower uses per minute
- \(\text{shower time}\) = How long the shower runs in minutes
- \(\text{water used}\) = Total water consumed for the bath or shower
- \(\text{difference}\) = How much more one option uses than the other
Step by step method
- Multiply the bath fill rate by the bath time to get total bath water used.
- Multiply the shower flow rate by the shower time to get total shower water used.
- Compare the two totals.
- Subtract the smaller total from the larger total to find the difference.
Worked example
Here is a simple example comparing a standard bath with a short shower.
- A bath fills at 10 liters per minute for 8 minutes, so the bath uses \(10 \times 8 = 80\) liters.
- A shower flows at 8 liters per minute for 6 minutes, so the shower uses \(8 \times 6 = 48\) liters.
- Compare the totals: 80 liters versus 48 liters.
- The difference is \(80 - 48 = 32\) liters.
Answer. The bath uses 80 liters, the shower uses 48 liters, and the bath uses 32 liters more.
Tips and common mistakes
- Make sure both inputs use the same units, such as liters and minutes or gallons and minutes.
- Do not compare a full bath with only part of a shower unless you are using the same time basis.
- If your showerhead has a known flow rate, use that instead of guessing.
- Remember that bath tubs can vary a lot, so the fill rate and time matter.
Frequently asked questions
What is a typical shower flow rate?+
Standard heads use ~9 L/min; low-flow heads ~6 L/min.
How big is an average bath?+
Around 100 to 150 litres when filled to a normal level.
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