A full bath uses about 80–150 litres of water, while a standard shower uses about 9 litres (2.4 gallons) a minute and a low-flow head 6 litres. So a quick shower almost always uses less – but a long power shower can use more than a bath. Heating that water is usually the bigger cost.
How to use the Bath vs Shower Calculator
- Shower flow rate
- Shower length
- Bathtub capacity
- Bath fill level
- Body weight
- Washes per week
- Water and sewer price
- Cost to heat 100 L of water
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter your shower’s flow rate and typical length, the tub capacity and how full you fill it, your body weight, how many times a week you wash, and your water and energy prices.
Tips
- Use the amounts printed on the product (ml, sheets, applications) where available.
- Count everyone in the household who shares the product.
- Buy a little extra so you never run out unexpectedly.
- Small daily habits add up – check the yearly figures for the real impact.
Common mistakes to avoid
- Forgetting that hot water costs energy as well as water.
- Underestimating how much sunscreen a full application needs.
- Comparing pack prices without checking the size of each pack.
Inputs explained
| Field | What to enter |
|---|---|
| Shower flow rate | Units: gpm, L/min |
| Shower length | In min |
| Bathtub capacity | Units: L, US gal |
| Bath fill level | Choose one: Full, Three quarters, About 60%, Half … |
| Body weight | Units: kg, lb, g |
| Washes per week | A number |
| Water and sewer price | Units: /m³, /1000 US gal |
| Cost to heat 100 L of water | Amount in your currency |
What each result means
- Water per shower = [Shower flow rate]×[Shower length]×60
- Water per bath = max([Bathtub capacity]×[Bath fill level] – [Body weight]÷1000, 0)
- Bath minus shower = [Water per bath] – [Water per shower]
- Showers – water per year = [Water per shower]×[Washes per week]×52.18
- Baths – water per year = [Water per bath]×[Washes per week]×52.18
- Showers – cost per year = [Showers – water per year]×([Water and sewer price] + [Cost to heat 100 L of water]×10)
- Baths – cost per year = [Baths – water per year]×([Water and sewer price] + [Cost to heat 100 L of water]×10)
Example values
How the main result changes when Shower flow rate changes and everything else stays at the example values above:
| Shower flow rate (gpm) | Bath minus shower (L) |
|---|---|
| 1.25 | 42.1 |
| 1.87 | 23.2 |
| 2.5 | 4.3 |
| 3.12 | -14.6 |
| 3.75 | -33.6 |
| 5 | -71.4 |
Formula
Shower water = flow rate × minutesBath water = tub capacity × fill level − water displaced by your body (≈ body weight ÷ 1 kg/L)Yearly = per wash × washes per week × 52.18Worked example
Inputs — Shower flow rate: 2.5 gpm; Shower length: 8 min; Bathtub capacity: 200 L; Bath fill level: Three quarters; Body weight: 70 kg; Washes per week: 7; Water and sewer price: $4 /m³; Cost to heat 100 L of water: $0.6.
Results — Water per shower = 75.7 L; Water per bath = 80 L; Bath minus shower = 4.3 L; Showers – water per year = 27.7 m³; Baths – water per year = 29.2 m³; Showers – cost per year = $276.53; Baths – cost per year = $292.21.
Frequently asked questions
Does a shower use less water than a bath?
Usually – an 8-minute shower at 2.5 gpm uses about 76 L, while a 60%-full bath uses 100–120 L.
How much water does a bath use?
80–150 L (20–40 gallons) depending on the tub and how full you fill it.
How can I use less water in the shower?
Fit a low-flow head (1.5–1.8 gpm) and keep showers under 5 minutes.
What formula does the Bath vs Shower Calculator use?
Shower water = flow rate × minutes.