# How Long Does It Take For Water To Boil?

In order to boil water, one has to increase the temperature of water to its boiling temperature at normal atmospheric pressure, and this requires energy.

The most common ways of boiling water include heating it on the stove, in the microwave, or in the electric kettle. There are other ways of boiling the water, for example, in the electric oven, but they are rarely used.

Updated: March 17, 2023.

## How Much Energy Is Needed To Boil The Water?

In order to boil water, one needs the energy to increase its temperature.

The exact energy requirement is easy to calculate, at least in theory.

Water heat capacity is 4.2 kJ/°Ckg, meaning that it takes 4.2 kJ (kilo-Joules) of energy to raise the temperature of a kilogram of water by 1°C.

If the water temperature is 20°C (68°F), to boil 1 (one) liter (4 cups) of water, one needs:

E = 4.2 * 1 * (100 – 20) = 336 kJ

So, in theory, to raise the temperature of 1 liter (4 cups) of water by 80°C, one needs 336 kJ of energy.

## How Long Does It Take to Boil Water?

In the case of an ideal heater, to boil 1 liter (4 cups) of water at 20°C (68°F), the boiling time is:

Time = Required Energy / Power of the heater

For example:

• 0.75 kW heater → T = 336 kJ / 0.75 kW = 448 seconds = 7 min 28 seconds
• 1 kW heater → T = 336 kJ / 1 kW = 336 seconds = 5 min 36 seconds
• 2 kW heater → T = 336 kJ / 2 kW = 168 seconds = 2 min 48 seconds

For 1 cup (250 ml) of water, boiling time is four times shorter (750W heater ~112 seconds, 1 kW heater ~84 seconds, 2 kW heater ~42 seconds, etc.).

However, in real life, plenty of energy is lost because of converting one form of energy (for example, electricity) into another form of energy (thermal energy of water), energy losses because the heater has to heat the water container and the heater itself, etc.

On average, to boil water, it takes:

- 1500W microwave: 1-1.5 min cup (250 ml) of water,

- 700-800W microwave: 2.5-3 min cup (250 ml) of water,

- gas stove: 6-8 min 1 liter (four 250 ml cups) of water,

- electric stove: 8-12 min 1 liter (four 250 ml cups) of water,

- induction cooktop: 5-6 min 1 liter (four 250 ml cups) of water,

- 1500W kettle: ~4 min 1 liter (four 250 ml cups) of water,

- 2500W kettle: 2-3 min 1 liter (four 250 ml cups) of water, etc.

In order to speed up things, one can use a closed water container (it must NOT be a sealed container, or it may blow up due to the pressure inside!), a stronger water heater, a smaller amount of water, etc.

## Boil Water in a Microwave

A microwave oven is one of the most efficient means of boiling water, but one has to be very careful.

Note: before boiling water in a microwave, it is highly recommended to read the microwave's Owner's Guide, especially Safety Issues and Boiling Water/Liquids, just in case.

When boiling water in a microwave, always use microwave-safe pots/cups - never use metal ones and never use lids.

Another very interesting but also very dangerous issue is - water overheating.

The microwave heats water very quickly, and usually, one uses cups with very smooth surfaces - steam bubbles usually need some surface imperfection to cling to when forming.

All of this leads to superheated water - water with a temperature above its boiling point but with no steam bubbles.

But, as soon as the user touches the pot/cup with the superheated water, a large number of bubbles may form almost instantly - hot steam bursts, causing burns on the unprotected skin.

For short, be very careful when boiling the water with a microwave.

But, on average, in order to boil water, it takes 1500W microwave 1-1.5 min to boil a cup (250 ml) of water, and 700-800W microwave 2.5-3 min to boil a cup (250 ml) of water.

## Boil Water in Electric Kettle

Electric kettles are designed to boil water as quickly as possible.

On average, to boil 1 liter of water, a 1500W kettle requires ~4 min, and a 2500W kettle requires 2-3 min.

An electric kettle is not as efficient a heater as a microwave oven since there is a large "parasite" mass to be heated, but there is no danger of superheating the water.

Personally, if You have the need to quickly boil various amounts of water for coffee, tea, and similar, an electric kettle is a way to go.

## Benefits Of Boiling Water

There are many benefits of boiling water, regardless of whether You are at home or outdoors.

Boiling water can be used for making various drinks and for preparing food.

Also, tap water is not always safe to drink - boiling it can kill viruses, bacteria, and other pathogens, making it safe for humans to drink.

## How Long to Boil Water to Make It Safe?

The boiling temperature of the water is 100°C (212°F) - at atmospheric pressure of 1 bar (1 kg per 1 cm2), which is more or less atmospheric pressure at sea level.

As the height is increased, the water boiling temperature decreases.

For example: to make water safe for drinking, it is recommended to boil water at sea level for 1 minute (60 seconds), but at an altitude of 2000m (6557 ft) where water boiling temperature is ~199.4°F (~93°C), it is recommended to boil it for 3 minutes (180 seconds).

## Water Boiling Temperature vs. Altitude

The following chart lists the boiling temperatures of water (given in °F and °C) according to the altitude (given in feet and meters). As a reference, several cities and well-known places with their altitudes are also shown in the chart.

 Altitude Boiling Temperature Feet Meters Fahrenheit °F Celsius °C Dead Sea, Jordan/Israel: -1414 feet (-431 meters) -1000 -305 213.9 101.1 -750 -229 213.5 100.8 -500 -152 213.0 100.5 Qattara Depression, Egipt: -435 feet (-133 meters) -250 -76 212.5 100.3 0 (Sea Level) 0 (Sea Level) 212.0 100.0 250 76 211.5 99.7 500 152 211.0 99.5 750 229 210.5 99.2 1000 305 210.1 98.9 Phoenix, Arizona: 1160 feet (353.8 meters) 1250 381 209.6 98.6 1500 457 209.1 98.4 1750 533 208.6 98.1 2000 610 208.1 97.8 2250 686 207.6 97.6 Tuscon, Arizona: 2389 feet (728 meters) 2500 762 207.2 97.3 2750 838 206.7 97.1 3000 914 206.2 96.8 3250 991 205.7 96.5 3500 1067 205.3 96.3 El Paso, Texas: 3740 feet (1140 meters) 3750 1143 204.8 96.0 4000 1219 204.3 95.7 4250 1295 203.8 95.5 4500 1372 203.4 95.2 4750 1448 202.9 94.9 5000 1524 202.4 94.7 5250 1600 202.0 94.4 Denver, Colorado: 5280 feet (1610 meters) 5500 1676 201.5 94.2 5750 1753 201.0 93.9 6000 1829 200.6 93.6 6250 1905 200.1 93.4 6500 1981 199.6 93.1 6750 2057 199.2 92.9 Flagstaff, Arizona: 6901 feet (2106 meters) 7000 2134 198.7 92.6 7250 2210 198.2 92.4 7500 2286 197.8 92.1 7750 2362 197.3 91.8 8000 2438 196.9 91.6 8250 2515 196.4 91.3 8500 2591 196.0 91.1 8750 2667 195.5 90.8 9000 2743 195.0 90.6 9250 2819 194.6 90.3 9500 2896 194.1 90.1 9750 2972 193.7 89.8 10000 3048 193.2 89.6 10250 3124 192.8 89.3 Alma, Colorado: 10361 feet (3158 meters) 10500 3200 192.3 89.1 10750 3277 191.9 88.8 11000 3353 191.4 88.6 11250 3429 191.0 88.3 11500 3505 190.5 88.1 11750 3581 190.1 87.8 12000 3658 189.7 87.6 12250 3734 189.2 87.3 12500 3810 188.8 87.1 12750 3886 188.3 86.8 13000 3962 187.9 86.6 13250 4037 187.4 86.4 13500 4115 187.0 86.1 13750 4191 186.6 85.9 14000 4267 186.1 85.6 14250 4343 185.7 85.4 14500 4420 185.3 85.1 14750 4496 184.8 84.9 15000 4572 184.4 84.7 15250 4648 184.0 84.4 15500 4724 183.5 84.2 15750 4801 183.1 83.9 Mont Blanc, France: 15764 feet (4808 meters) 16000 4877 182.7 83.7 16250 4953 182.2 83.5 16500 5029 181.8 83.2 16750 5105 181.4 83.0 17000 5182 180.9 82.7 17250 5258 180.5 82.5 17500 5334 180.1 82.3 17750 5410 179.7 82.0 18000 5486 179.2 81.8 18250 5563 178.8 81.6 18500 5639 178.4 81.3 18750 5715 178.0 81.1 19000 5791 177.6 80.9 19250 5867 177.1 80.6 19500 5944 176.7 80.4 19750 6020 176.3 80.2 20000 6096 175.9 79.9 20250 6172 175.5 79.7 Denali, Alaska: 20310 feet (6190 meters) 20500 6248 175.1 79.5 20750 6325 174.7 79.3 21000 6401 174.2 79.0 21250 6477 173.8 78.8 21500 6553 173.4 78.6 21750 6629 173.0 78.3 22000 6706 172.6 78.1 22250 6782 172.2 77.9 22500 6858 171.8 77.7 22750 6934 171.4 77.4 23000 7010 171.0 77.2 23250 7087 170.6 77.0 23500 7163 170.2 76.8 23750 7239 169.8 76.5 24000 7315 169.4 76.3 24250 7391 169.0 76.1 24500 7468 168.6 75.9 24750 7544 168.2 75.6 25000 7620 167.8 75.4 25250 7696 167.4 75.2 25500 7772 167.0 75.0 25750 7849 166.6 74.8 26000 7925 166.2 74.5 26250 8001 165.8 74.3 26500 8077 165.4 74.1 26750 8153 165.0 73.9 27000 8230 164.6 73.7 27250 8306 164.2 73.5 27500 8382 163.8 73.2 27750 8458 163.4 73.0 28000 8534 163.1 72.8 28250 8611 162.7 72.6 28500 8687 162.3 72.4 28750 8763 161.9 72.2 29000 8839 161.5 72.0 Mount Everest, Himalayas: 29010 feet (8848 meters) 29250 8916 161.1 71.7 29500 8992 160.7 71.5 29750 9068 160.4 71.3 30000 9144 160.0 71.1

Thus, if you want to boil water for cooking or drinking at higher altitudes, perhaps it is better to use a pressure cooker and boil water for a shorter period of time.

## Energy Sources in Emergencies

In emergencies and similar situations, one of the first things that are gone is - electric energy.

To boil water, one can use a gas stove (if it works properly without electricity - these days, there are even models that don't function properly without electricity, although their main energy source is gas!), a fire pit, or anything similar.

But, one can also use a microwave or electric kettle if one has:

A solar Generator/Power Station can be used to power a microwave oven or electric kettle if the output power of the power station is stronger than the microwave oven/electric kettle's required power.

This means that power stations in the 1500-2000 watts range can be used to power microwaves and electric kettles in the 1200-1500 watts range.

To boil a cup of water (250 ml), a 1500W electric kettle requires ~1 minute, while a 1500W microwave requires 1-1.5 minutes.

Since power stations feature an average energy efficiency of ~85%, boiling a cup of water using a 1500W electric kettle requires ~30 Wh of energy:

E(electric kettle) = 1500W * 60s = 90000 Ws = 25 Wh

E(battery) = E(electric kettle) / 0.85 = 29.4 Wh (~30 Wh)

Most power stations/solar generators in the 1500-2000W range feature internal batteries being able to store 500 - 2000 Wh of energy.

For example, a power station having a 900Wh internal battery is able to boil 30 cups (250 ml) of water - having warm tea, coffee, soup, or similar drink/food can be extremely important in emergencies or when camping, hiking, and similar. Of course, hot water has other purposes as well, not just for cooking and drinking.

Similarly to power stations, one can use a large, deep discharge battery and power inverter to power a microwave oven or electric kettle to boil water, as long as the output power of the power inverter is stronger than the required power of microwave oven and/or electric kettle.

Portable power generators may be used directly to power the microwave ovens and/or electric kettles to boil water as long as the output power of the power generator is stronger than the microwave oven and/or electric kettle.

## Water Boiling Frequently Asked Questions

Here are some of the most popular Frequently Asked Questions (FAQ) about boiling water:

### How do you know when water is fully boiled?

When water is boiling, one can see bubbles of water steam exiting the water.

### Why does boiling water take so long?

It takes time to transfer heat to the water required for increasing the temperature of the water.

Depending on the heat source and its power, the amount of water, the initial temperature of the water, and altitude, water can boil rather quickly, but also, it can take some time.

### How long does it take for water to come to a rolling boil?

When water starts to boil using a very strong heat source, water can start to boil rather quickly.

If that heat source continues to heat the water, a rolling boil occurs - a very strong, vigorous boil with plenty of bubbles and very active and energetic bubbles motion.

### Does adding salt make water boil faster?

In real life - no.

Adding salt to the water decreases the water's heat capacity, but it also increases the water's boiling point.

So, in real life, the difference between boiling pure water and the same amount of water with some salt added is a few seconds, even if that.

### How do you make water boil faster?

One can make water boil faster by using a stronger heat source, using less water, or using water with a higher initial temperature.

### How does a rolling boil work?

When the water is heated using a very strong heat source, which causes a very strong, vigorous boil with plenty of bubbles and very active and energetic bubbles motion - that is a rolling boil.