Bath vs. Shower Cost Calculator
Enter your fixture flow, bath fill, temperatures, and utility rates to compare one bath with one shower. The result separates water use from the energy needed to heat it and gives the shower duration where the costs meet.
Cheaper optionShower is cheaper by $0.67 per use
- Shower water used
- 16.8
- Bath water used
- 35
- Cost per shower
- $0.66
- Cost per bath
- $1.33
- Break-even shower duration
- 16.0 minutes
- Annual cost difference
- $242.70
- Annual water difference
- 6,624.8
Includes volume-based water and sewer charges plus energy needed to heat the delivered water.
Fixed utility charges, pipe losses, heater standby losses, and hot-water pipe purge volume are excluded.
How to use this calculator
- Enter the minutes that shower water runs and the showerhead flow rate.
- Enter the gallons you actually put in the bath, rather than the tub’s full capacity.
- Use your incoming cold-water and delivered bath and shower temperatures.
- Choose the heater fuel, then enter its thermal efficiency and the matching energy price.
- Add the volume-based water and sewer rate and the number of weekly uses to see annual differences.
How the bath and shower costs are calculated
A shower uses water at a rate, while a bath uses the volume you put in the tub. Shower volume is Vs = q × t, where q is gallons per minute and t is minutes. Bath volume is the entered fill volume Vb. Both volumes are charged at the combined water and sewer rate divided by 1,000.
The calculator also estimates the fuel needed to raise each gallon from incoming cold-water temperature to its delivered temperature. The heat needed is Q = 8.345 × V × max(T − Tc, 0) Btu. The 8.345 factor is the approximate weight of a gallon of water in pounds, and each pound needs about one Btu to rise one degree Fahrenheit.
Fuel energy is E = Q ÷ (η × F), where η is heater efficiency as a decimal and F is 3,412 Btu per kWh for electricity or 100,000 Btu per therm for natural gas. The per-use cost is C = V × w + E × p, with w as the water-and-sewer cost per gallon and p as the energy price.
Finding the break-even shower duration
The break-even duration is the bath’s total cost divided by the shower’s cost per minute. In full, t* = [Vb × w + 8.345 × Vb × max(Tb − Tc, 0) × p ÷ (η × F)] ÷ [q × w + 8.345 × q × max(Ts − Tc, 0) × p ÷ (η × F)]. A shower shorter than that point costs less under the entered assumptions; a longer one costs more.
Flow rate and bath fill volume usually move the water result most. Temperature rise, heater efficiency, fuel type, and energy price matter more when heating is a large part of the bill. Enter seasonal cold-water temperature if you want to compare winter and summer conditions. A gas price must be dollars per therm, while an electric price must be dollars per kWh.
What this comparison leaves out
This is an operating-cost estimate for water and water heating. It excludes fixed utility charges, hot-water pipe purge volume, pipe heat loss, heater standby losses, and variation in appliance efficiency while it cycles. It also treats bath temperature as one average temperature even though bath water can cool during filling and soaking.
Worked example
For an 8-minute shower at 2.1 gallons per minute, shower water use is 2.1 × 8 = 16.8 gallons. With 55 F incoming water, a 105 F shower, 90% efficient electric heat at $0.18 per kWh, and water and sewer at $15 per 1,000 gallons, the shower costs about $0.66.
A 35-gallon bath at 102 F under those same assumptions costs about $1.33. The shower is about $0.67 cheaper each time. The break-even shower duration is about 16.0 minutes, and choosing the cheaper option seven times a week changes annual operating cost by about $243.
Common questions
Is a bath or shower usually cheaper?
A short shower is often cheaper because it uses less water than a typical bath. The answer changes with showerhead flow, bath fill volume, temperature, and local water and energy prices. A long high-flow shower can cost more than a partially filled bath.
How long can I shower before it uses as much water as a bath?
Divide the bath fill volume by the showerhead flow rate. For example, a 35-gallon bath and a 2.1-gallon-per-minute showerhead use the same water after about 16.7 minutes. Cost break-even can differ because bath and shower temperatures may not be the same.
How do I measure my showerhead flow rate?
Use the flow rate printed on the showerhead when it is available. Otherwise, collect the water in a marked container for 30 or 60 seconds while the shower is set as normally used, then convert that volume to gallons per minute. Repeat the test if household pressure varies noticeably.
How do I estimate the gallons used to fill my bathtub?
If you know the tub’s dimensions, calculate the water volume to the normal fill line rather than to the rim. You can also time the tub faucet and multiply its measured gallons-per-minute flow by filling time. Include only the water you use for the bath, not the tub’s advertised capacity.
Why do water temperature and heater efficiency affect the comparison?
Heating colder incoming water to a hotter delivered temperature needs more energy. A less efficient heater must buy more fuel to supply the same heat. These effects can make two fixtures with similar water use have different operating costs.
Does a gas water heater make baths cheaper than an electric heater?
Not automatically. Natural gas and electricity use different billing units and heaters can have different thermal efficiencies. Enter the price shown on your bill in dollars per therm or dollars per kWh, as appropriate, to compare your own operating costs.