What is 30 Degree Celsius in Fahrenheit?

 

30 degrees Celsius is 86 degrees Fahrenheit. Not approximately: exactly. The formula is F = (C × 9/5) + 32, so 30 × 9/5 = 54, and 54 + 32 = 86.

Book FREE Math Trial Classes Now!

Celsius and Fahrenheit are the two main temperature scales in everyday use. Fahrenheit is standard in the United States and Celsius nearly everywhere else, so travellers, students and anyone reading a foreign weather forecast ends up converting between them. Below is the working, a full table, a way to do it in your head that is exact rather than approximate, and why two scales exist at all.

The formula for converting Celsius to Fahrenheit

F = (C × 9/5) + 32

Nine fifths is the same as 1.8, so you may also see it written F = (C × 1.8) + 32. Both give the same answer.

Step 1. Multiply the Celsius value by 9/5.

30 × 9/5 = 54

Step 2. Add 32.

54 + 32 = 86

So 30 degrees Celsius is equivalent to 86 degrees Fahrenheit. The two parts of the formula do two different jobs: multiplying by 9/5 stretches the scale, because a Celsius degree is larger than a Fahrenheit degree, and adding 32 shifts the zero point, because the two scales do not start in the same place.

Celsius to Fahrenheit conversion table

How to convert in your head, exactly

The usual shortcut is to double the Celsius number and add 30. It is quick and it is wrong by a growing amount: at 20°C it is out by 2, at 30°C by 4, and at 40°C by 6. For this page's own question it gives 90 instead of 86.

There is a version that is exact and barely harder:

Double it, take off 10%, then add 32.

That works because doubling and then removing a tenth leaves you with 1.8 times the original, which is exactly 9/5. Nothing is approximated.

• 30°C: double is 60, minus 6 is 54, plus 32 is 86°F.
• 20°C: double is 40, minus 4 is 36, plus 32 is 68°F.
• 35°C: double is 70, minus 7 is 63, plus 32 is 95°F.

If you only want a rough figure, stop after doubling and adding 30, but remember it runs high, and by more the hotter it gets.

What 30 degrees Celsius actually feels like

30°C is warm weather, the kind associated with summer and with tropical regions. It is the point at which people look for shade, cold drinks or a beach.

• An air-conditioned room usually sits between 68°F and 72°F, which is 20°C to 22°C.
• A hot summer day runs from roughly 85°F to 100°F, which is about 29°C to 38°C.

So 30°C, or 86°F, sits at the lower edge of what most people call hot without being uncomfortable. It is sunscreen weather, and the kind of day where outdoor activity is easier in the early morning or the evening.

Where this conversion gets used

• Travel: moving between a Celsius country and a Fahrenheit one, the forecast is useless until you can convert it. Knowing 30°C is 86°F decides what goes in the suitcase.
• Cooking: most recipes now give both, but an older recipe or a single-scale thermometer still forces the conversion.
• Science and school: temperature conversion is a standard skill in geography, physics and chemistry, and it is one of the clearest examples of why measurement systems differ at all.

Three mistakes that give the wrong answer

• Doing the two steps in the wrong order. Going from Celsius you multiply first and add second. Going the other way you subtract first and multiply second. Swapping the order changes the answer: for 30°C, (30 × 9/5) + 32 is 86, while (30 + 32) × 9/5 is 111.6.
• Using 5/9 instead of 9/5. They look alike and they do opposite jobs. Celsius to Fahrenheit stretches the number, so the fraction must be bigger than 1.
• Assuming negatives behave differently. They do not. −10°C is 14°F by the same formula: −10 × 9/5 is −18, and −18 + 32 is 14.

One oddity worth knowing, because children find it satisfying: at −40 the two scales agree. −40°C is −40°F. It is the single temperature where converting changes nothing, and it is a good way to check that a formula has been applied correctly.

What grade is this at school?

Converting with a formula like this is Grade 6 work. Common Core standard 6.EE.A.2.c asks students to "evaluate expressions at specific values of their variables" and specifically to "include expressions that arise from formulas used in real-world problems". F = (C × 9/5) + 32 is exactly that kind of formula. Source: Common Core State Standards, Mathematics.

The useful thing for a parent helping with homework is that this is not a fact to memorize. A child who understands that the 9/5 stretches the scale and the 32 shifts its starting point can convert any temperature, and can work backwards too. A child who has memorized "30 is 86" can answer one question.

Why are there two temperature scales?

Celsius. Created in 1742 by the Swedish astronomer Anders Celsius, the scale is anchored to water: 0°C is where it freezes and 100°C is where it boils, at sea level. Those round numbers and the fit with the metric system are why it is used in science and in most of the world.

Fahrenheit. Developed in 1724 by the physicist Daniel Gabriel Fahrenheit, this scale was anchored to different reference points: the freezing point of a brine solution at 0°F, and approximate human body temperature at 96°F, a figure later refined to 98.6°F. It remains in everyday use in the United States and its territories.

This is why the conversion needs both a multiplication and an addition. The two scales disagree about the size of a degree and about where zero should sit. Being able to move between them quickly makes weather forecasts, recipes and medical readings from either system readable, and you can read more in our full Celsius to Fahrenheit guide.

Book FREE Math Trial Classes Now!

Questions parents ask

What is 30 degrees Celsius in Fahrenheit?

30 degrees Celsius is exactly 86 degrees Fahrenheit. Using the formula F = (C × 9/5) + 32: multiply 30 by 9/5 to get 54, then add 32 to get 86. There is no rounding involved, because 30 × 9/5 lands on a whole number.

What is a quick way to convert Celsius to Fahrenheit?

Double the Celsius value, take off 10%, then add 32. For 30°C: 60, minus 6 is 54, plus 32 is 86°F. This gives the exact answer, because doubling and removing a tenth is the same as multiplying by 1.8, which is 9/5.

Why does the usual "double it and add 30" trick not work?

Because it uses 2 in place of 1.8, so it overshoots by 0.2 for every degree Celsius. At 20°C it is 2 too high, at 30°C it is 4 too high, and at 40°C it is 6 too high. It is fine for a rough sense of the weather, but it is not the conversion.

Is 30 degrees Celsius hot?

Yes, 30°C or 86°F is generally considered warm to hot, and is typical of summer weather. For comparison, an air-conditioned room is usually 20°C to 22°C, and a hot summer day can reach 38°C, which is about 100°F.

Why are there two temperature scales?

They were built for different purposes and never merged. Celsius, from 1742, is anchored to water freezing and boiling, which suits the metric system and science. Fahrenheit, from 1724, was anchored to a brine solution and body temperature, and is still standard in everyday use in the United States.

Where is Fahrenheit used?

Primarily in the United States and its territories, along with a small number of other places. Almost everywhere else uses Celsius for weather and daily life, and Celsius or Kelvin in scientific work.

How do I convert Fahrenheit back to Celsius?

Reverse the two steps: subtract 32 first, then multiply by 5/9. For 86°F: 86 minus 32 is 54, and 54 × 5/9 is 30°C. The order matters, because subtracting after multiplying gives the wrong answer.

Related Articles

1. Multiplication and Division of Decimals
2. Top Resources to Learn Math Online
3. Choosing the Best Math Program for Your Child's Academic Growth
4. What You Need to Know About the International Math Kangaroo Contest?