Weather and Natural Phenomena


Wind Speed


Freezing and Boiling points of water

Convert between Fahrenheit and Celsius

Approximate conversion
Old Beaufort Scale - land

Old Beaufort Scale - sea

New Beaufort Scale



Temperature scaleFreezing point of waterBoiling point of waterDegrees between the two
Fahrenheit32 deg F212 deg F180
Celsius0 deg C100 deg C100
Kelvin273.15 K373.15 K100
Rankine491.67 deg Ra671.67 deg Ra180
Réaumur0 deg Ré80 deg Ré80
Rĝmer7.5 deg Rĝ60 deg Rĝ52.5
Newton0 deg N33 deg N33
Delisle150 deg De0 deg De-150

The usual symbol for temperature is ° (as in 20° C), but I'm not sure if all browsers will display that!

The old way of measuring temperature in Britain was Fahrenheit. Even when Celsius became the official way of measuring temperature, for example in weather forecasts, the forecasters still gave the Fahrenheit as well for many years. Even today, they sometimes give Fahrenheit to emphasise a particular extreme temperature. The rather odd figure for freezing point in Fahrenheit (32 deg F) is because 0 deg F is the temperature that brine (salt and water) freezes. That was the coldest the inventor, Fahrenheit, could reliably reproduce in his laboratory. The 180 gap was chosen because it has lots of factors. It can be divided by 2, 3, 4, 5, 6, 9, 10, etc.

The old name for Celsius was Centigrade. They are exactly the same values. The original scale invented by Celsius had the same size degree, but went the other way, so 100 degrees was freezing and zero degrees was boiling.

Kelvin is another way to measure temperature, used by scientists. 0 K is absolute zero, the coldest temperature that is theoretically possible (and impossible to achieve), which is -273.15 degrees Celsius. One degree in the Kelvin scale is the same step as one degree Celsius. Similarly Rankine starts at absolute zero as 0 deg Ra, and one degree in the Rankine scale is the same step as one degree Fahrenheit.

The other scales are historic ones and no longer used. The Réaumur scale used to be used in Europe, particularly in France and Germany, but was eventually replaced by the Celsius scale. Monsieur René de Réaumur proposed it in 1731. Rĝmer is a disused temperature scale named after the Danish astronomer Ole Christensen Rĝmer, who proposed it in 1701. It is similar to Fahrenheit in that the freezing point of brine is zero. Isaac Newton devised his scale around 1700. He invented the word 'thermometer' for an instrument to measure it. The Delisle scale was invented in 1732 by the French astronomer Joseph-Nicolas Delisle, and recalibrated in 1738. It remained in use for almost 100 years in Russia. Like the original Celsius, it goes the 'wrong' way.

The BBC programme QI (which stands for Quite Interesting) has pointed out that Briritsh people tend to use Celsius when talking about cold temperatures ("It was minus four last night.") but Fahrenheit for hot temperatures ("The temperature must be in the nineties today.") It is quite true. It somehow doesn't seem as impressive to talk about "the high twenties" (deg C) as a hot temperature or "twenty five" (deg F) as a cold temperature. This could be because a temperature in the twenties is ambiguous - both Celsius and Fahrenheit occur in Britain, in cold winters and hot summers (all right - we have a temperate climate!) It is also true that you can detect a ten degree Fahrenheit difference of temperature. A summer day in the seventies is distinctly cooler than a summer day in the eighties. To talk of "low twenties" and "high twenties" doesn't give the same distinction. On the other hand, it is definitely gratifying to high-light below freezing as negetive. Body temperature is also more impressive as Fahrenheit ("I have a temperature of over a hundred!")

Talking of which, an important fact is that normal body temperature in Fahrenheit is 98.6 deg F, and in Celsius, it is 37 deg C. I am NOT going to give it for the other scales!

There are other cases of mixed units. In
volume, the British drink pints of beer and milk, yet all other liquids are sold by litre (fruit juice, wine, water, petrol, etc.) We measure small lengths in millimetres, but large distances in miles. We measure our food in kilogrammes and ourselves in stone and pounds. Either we are very stupid, or very clever!

Accurate conversion of temperature (2 methods)
between Fahrenheit and Celsius

Fahrenheit to Celsius Celsius to Fahrenheit Fahrenheit to Celsius Celsius to Fahrenheit
Subtract 32
Multiple by 5
Divide by 9
Gives Celsius
Multiple by 9
Divide by 5
Add 32
Gives Fahrenheit
Add 40
Multiple by 5
Divide by 9
Subtract 40
Gives Celsius
Add 40
Multiple by 9
Divide by 5
Subtract 40
Gives Fahrenheit

The second method takes more steps, but has a pleasing symmetry. It comes from the completely useless piece of information

-40 deg C = -40 deg F

A correspondent has added these pleasing palindromes (reversals):

16 deg C = 61 deg F
28 deg C = 82 deg F

Approximate Fahrenheit and Celsius conversion

The problem with accurate conversions is that the calculations can be hard to do unless you have a calculator handy. Anyway, the answer tends to have decimals in, whereas most of us just want to know whether tomorrow's weather forecast is hot or cool! So here is a very rough approximation, within 5 deg C.

32 deg F0 deg C
40 deg F5 deg C
50 deg F10 deg C
60 deg F15 deg C
70 deg F20 deg C
80 deg F25 deg C
90 deg F30 deg C
Another way of doing this -

To convert from Fahrenheit to Celsius:
Subtract 30 and divide by 2.

To convert from Celsius to Fahrenheit:
Multiply by 2 and add 30.

I give the accurate value for the freezing point of water, because I am a gardener, so I think that frosts are IMPORTANT!

If you find the above table too hard to memorise, then remember that 70 deg F is 20 deg C, and this is a comfortable indoor room temperature. For temperatures above or below that, remember that 5 deg C is (roughly) 10 deg F. So 50 deg F (cool) is 10 deg C, and 90 deg F (hot - for Britain!) is 30 deg C.

The Beaufort scale was devised in 1805.

Old Beaufort Scale of Winds (Land)

ForceWindEffect on landSpeed
miles per hour
0CalmSmoke raises verticallyLess than 1
1Light airDirection shown by smoke but not by wind vanes1-3
2Light breezeWind felt on face; wind vanes move4-7
3Gentle breezeLeaves and twigs in motion; wind extends light flag8-12
4Moderate breezeRaises dust, loose paper and moves small branches13-18
5Fresh breezeSmall trees in leaf begin to sway19-24
6Strong breezeLarge branches in motion; whistling in telegraph wires;
difficulty with umbrellas
7Moderate galeWhole trees in motion; difficult to walk against wind32-38
8Fresh galeTwigs break off trees; progress impeded39-46
9Strong galeSlight structural damage occurs;
chimney pots and slates blown off
10Whole galeTrees uprooted and considerable structural damage55-63
11StormWidespread damage, seldom experienced in England64-75
12HurricaneWinds of this force only encounted in tropical revolving stormsMore than 75

This was copied from an old reference book. Note that it confidently states that you don't get hurricane force winds except in tropical revolving storms, and even force 11 is seldom found in England. Global warming seems to be proving that wrong. But I find the descriptions vivid, and you can use them today to estimate wind speed.

Old Beaufort Scale of Winds - Sea

in knots
0<1Calm, sea like a mirror.
11-3Light air, ripples only.
24-6Light breeze, small wavelets (0.2m). Crests have a glassy appearance.
37-10Gentle breeze, large wavelets (0.6m), crests begin to break.
411-16Moderate breeze, small waves (1m), some white horses.
517-21Fresh breeze, moderate waves (1.8m), many white horses.
622-27Strong breeze, large waves (3m), probably some spray.
728-33Near gale, mounting sea (4m) with foam blown in streaks downwind.
834-40Gale, moderately high waves (5.5m), crests break into spindrift.
941-47Strong gale, high waves (7m), dense foam, visibility affected.
1048-55Storm, very high waves (9m), heavy sea roll, visibility impaired. Surface generally white.
1156-63Violent storm, exceptionally high waves (11m), visibility poor.
1264+Hurricane, 14m waves, air filled with foam and spray, visibility bad.

Wave heights quoted are approximately those that may be expected in the open sea. In enclosed waters the waves will be smaller and steeper. Fetch, depth, swell, heavy rain and tide will also affect their height, and there will also usually be a time lag between any increase in the wind and the consequent increase in the sea.

New Beaufort Scale of Winds

The new scale has no names below Force 8, and they are slightly different anyway. The descriptions no longer exist. But the numbers and wind speeds are the same, except for force 12. I thought originally that this was a misprint in my reference book, but have since been informed that winds of hurricane strength had already been redefined as 115 KPH in the metric system by the time the new scale came out, which is 72 mph.

miles per hour
0 Less than 1
1 1-3
2 4-7
3 8-12
4 13-18
5 19-24
6 25-31
7 32-38
9Severe gale47-54
11Violent storm64-72
12Hurricane forceMore than 72


It may seem strange to put this on a weather page, but the descriptions are rather like the old Beaufort Scale, so I thought they belonged together.

1 detected only by seismographs< 3
2feeblejust noticeable by some people3 - 3.4
3slightsimilar to passing of heavy lorries3.5 - 4
4moderaterocking of loose objects4.1 - 4.4
5quite strongfelt by most people even when sleeping4.5 - 4.8
6strongtrees rock and some structural damage is caused4.9 - 5.4
7very strongwalls crack5.5 - 6
8destructiveweak buildings collapse6.1 - 6.5
9ruinoushouses collapse and ground pipes crack6.6 - 7
10disastrouslandslides occur, ground cracks and buildings collapse7.1 - 7.3
11very disastrousfew buildings remain standing7.4 - 8.1
12catastrophicground rises and falls in waves> 8.1


Wales as a unit of rainfall
Wales is well known as a unit of area (as in "a giant iceberg as big as Wales") - see
Length and Area for details. However, I have also heard of it as a unit of rainfall. Some rain forest was described as being "three times as wet as Wales".

The Misery Index - I couldn't resist this one!
The Misery Index was suggested in correspondence to the Times as a classification of the discomfort endured during a wet English summer. In this index, the balmy air and blue sky of the Mediterranean are indicated as 100. Values below 30 call for immediate emigration to escape from the grey skies and continuous rain in Britain.

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