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A standard bathtub filled to the overflow holds between 150 and 220 litres (40 to 58 US gallons) of water: the common 170 × 70 cm tub is rated at 183 litres — 48.3 gallons — on the manufacturer's spec sheet (Roca). The water you actually use for a bath is less, around 150 litres or 39.6 gallons, because nobody fills a tub to the brim and because your own body displaces about 70 litres. That is what the pictogram above draws: 75 people drinking for a day. Use the "Show" selector to see it in glasses or bottles instead.
Manufacturers publish the capacity on every model's spec sheet, so there is no need to estimate it. These are four catalogue tubs from Roca:
| Bathtub | Capacity |
|---|---|
| Steel, 150 × 70 cm | 153 litres (40.4 gal) |
| Steel, 170 × 70 cm (the common one) | 183 litres (48.3 gal) |
| Acrylic two-seater, 170 × 75 cm | 208 litres (54.9 gal) |
| Acrylic, 170 × 75 cm | 215 litres (56.8 gal) |
| This site's reference | 150 litres (39.6 gal) |
Big soaking and freestanding tubs go further: the US Environmental Protection Agency puts a full bath at up to 70 gallons (265 litres) against 10 to 25 gallons for a shower.
Measure a bathtub inside and treat it as a box and the number runs away from you. The 170 × 70 tub has an interior of 1.525 × 0.575 × 0.395 metres, which would be 346 litres… yet the maker rates it at 183: only 53 % of that. A tub is not a box. The backrest slopes, the bottom is narrower than the rim, the corners are rounded, and the water stops rising at the overflow, a few centimetres below the edge. That is why almost everybody overestimates how much water fits.
There is a second reason, and it is Archimedes: you take up room too. The human body is almost exactly as dense as water (one kilo per litre), so a 70 kg (155 lb) person displaces about 70 litres, roughly 18 gallons. Getting in raises the level by that much water you never had to run from the tap. So a normal bath — water at waist height, with you in it — uses on the order of 100 to 150 litres even in a tub rated for 215.
And since a litre of water weighs a kilo, those 150 litres are also 150 kilos (330 lb) of water resting on your bathroom floor, plus your own weight.
The honest answer is: it depends on your showerhead and how long you take. In the US the federal cap has been 2.5 gallons per minute since the Energy Policy Act of 1992, and WaterSense-labelled heads use no more than 2.0 gpm. Here is how many minutes of shower equal one bath:
| Shower flow | = 150 L / 39.6 gal bath | = 100 L / 26.4 gal bath |
|---|---|---|
| 1.5 gpm (efficient head) = 5.7 litres/min | 26.4 min | 17.6 min |
| 2.0 gpm (WaterSense limit) = 7.6 litres/min | 19.8 min | 13.2 min |
| 2.5 gpm (US federal maximum) = 9.5 litres/min | 15.9 min | 10.6 min |
In other words, with a standard 2.5 gpm head you would have to stand under it for 15.9 minutes to match a single bath — and with an efficient one, for 26.4. That is why the shower almost always wins in the US, and why EPA can say the average family uses nearly 40 gallons a day showering: the whole family's showers add up to about one bath.
You do not have to trust any average. Put a one-gallon jug under the shower running full and time how long it takes to fill:
gallons per minute = 60 ÷ seconds to fill the jug
If it fills in 24 seconds, your shower is 2.5 gpm; in 30 seconds, 2.0. With a 1.5-litre bottle the formula is litres per minute = 90 ÷ seconds. Once you know your flow, the table above stops being an estimate and becomes your number.
Click any figure to see it drawn to scale above:
The figure that really lands is the yearly one. Bathing every day comes to 54,750 litres a year (14,463 gallons), more than the 46,720 litres an average person uses at home in a whole year for everything else combined. Put another way: bathing daily uses more water than everything else you do at home put together.
Not much, if you mean the water: at about €2.02 per cubic metre — Spain's average, the reference this site uses — the 150 litres of a bath cost €0.30. Thirty cents.
The expensive part is heating it. Taking 150 litres from the 15 °C (59 °F) that comes out of the tap to a 40 °C (104 °F) bath needs about 4.4 kWh — one kilowatt-hour heats 860 litres by one degree — which costs several times the water itself, on gas or on electricity. The formula, if you want to run it at your own temperature: kWh = litres × degrees of rise ÷ 860. That is the real cost of a bath, and its carbon footprint too.
Want to visualize other amounts of water? Try the liters tool, or see how much an Olympic swimming pool holds. And if you are after areas or weights, there is the Hectareometer and the kilos tool.