Introduction: Be a Scientist: Make Your Own Thermometer

Picture of Be a Scientist: Make Your Own Thermometer

About 300 years ago, Daniel Fahrenheit made and calibrated the first reliable thermometers. Some people* still use the scale he developed; the Fahrenheit Scale.

*like Americans ;-)

Step 1: Materials and Tools.

Picture of Materials and Tools.

You need a small air-tight container (a 35mm film cannister is perfect), a thin translucent or transparent tube (such as an empty biro ink-tube), food colouring and something to make and seal a hole.

If you are going to add a scale, you will also need a piece of white card, clear sticky-tape and a narrow marker (an OHP pen is good).

Step 2: Make It.

Picture of Make It.

Make a small hole in the middle of the cannister's lid, put the tube through it and seal around the tube. When you put the lid back on, the tube should almost reach the bottom of the cannister, but not quite.

There are three ways to make the hole:

Drill really carefully: use a small sharp blade to drill a perfectly circular hole, stopping frequently to try the tube through it. When you can just get the tube through, stop drilling.

Drill quickly: use whatever tool you have handy - pocketknife, scissors, particle-beam accelerator - and then seal any gaps between the hole and the tube with blu-tac, modelling clay or hot-glue.

Melt it: heat a narrow nail in a flame (hold the nail with pliers or you'll burn yourself), and poke a hole in the middle of the lid. Quickly push the tube through the hole and, as the plastic cools, it will set and make an air-tight seal around the tube.


Did you push the tube too far through before you sealed it, and now you can't close the lid? Never mind, just snip the bottom of the tube off, no big deal.

Step 3: Fill It.

Picture of Fill It.

Fill the cannister about a third or half-full with coloured water and push the lid on.

Be careful, because the water can easily squirt out the top of the tube.

You should end up with the coloured water part-way up the tube with plenty of free space above it.

Step 4: Try It.

Picture of Try It.

That, basically, is that. The thermometer is finished and works.

Hold the cannister in your fist - the warmth of your hand will make the air in the cannister expand and push the water up the tube. Dip it in your coffee, it will go up further. Stand it in your fridge and the air will cool and contract, pulling the water back down.

Obviously you cannot use the thermometer to check your freezer compartment or your sauna (think about it...), but you are now the proud possessor of a working model of an early Fahrenheit thermometer.

Step 5: Calibrate It.

Picture of Calibrate It.

Thermometers aren't much use without a scale. You can have one as well.

Tape the card against the tube like a flag, then hold the cannister in your fist. When the water stops moving, mark the point and label it "hand heat". Try a range of other places - a cup tea just cool enough to drink, slip it under the quilt with your loved one in the morning. One of Fahrenheit's original standard points was "human armpit".

When you have enough points on your scale, add some numbers. It doesn't really matter what they are, either, since Fahrenheit's scale was quite arbitrary - he just used numbers that "felt" right, which is why water freezes at 32F and boils at 212F.

Give your scale a name, then take delight in confusing your friends when the conversation inevitably drifts round to the weather;

"Boy, it's hot today!"
"Yeh, it was nearly forty Desmonds when I checked this morning."


Ploopy made it! (author)2015-08-06


It works really well.

Ploopy (author)2015-08-05


Kiteman (author)Ploopy2015-08-05

Thank you!

fishhhhhhh_ (author)2014-12-08


Kiteman (author)fishhhhhhh_2014-12-08


argha halder (author)2013-07-11

great instructable and by the way i use farenhite scale.(more available in my country)

Kiteman (author)argha halder2013-07-11


argha halder (author)Kiteman2013-07-11

every day i search your name in the search bar and see some awesome instructables everytime!and keep commenting on them.hope many such instructables from you.(and keep replying to my comments and question. just saying!)

Kiteman (author)argha halder2013-07-11

You don't need to search, just click on my user name, or follow this link.

Fuzz2050 (author)2007-01-26

It might just be a rumor, but I heard the Fahrenheit scale isn't totally arbitrary, 0 degrees is supposed to be the coldest temperature you can achieve with salt and ice, and 100 is supposed to be body temperature. He was a little off, but there was still method to his madness.

infiniteregress (author)Fuzz20502007-01-26

I thought it was defined a bit more wackily... 99 is body temperature I thought? But I remember he defined 100 to be like, the temperature cow's milk comes out as or something... It's definitely defined along those lines

ilpug (author)infiniteregress2011-08-28

Average body temperature is 98.6 degrees Fahrenheit

jdoege (author)infiniteregress2007-01-27

Sort of. 0 was the coldest he could get fluid water with salt. 100 was supposed to be body temperature, but the subject he used, his wife, had a slight fever when he established the measure. Or so the story goes...

nc4tc (author)Fuzz20502009-07-25

You should read the story of how Fahrenheit determined his scale:
It is funny

account3r2 (author)2011-02-21

Some people* still use the scale he developed; the Fahrenheit Scale.

*like Americans (me!)  :D

BSG (author)2009-03-09

BTW: This thing is called a thermo"meter", not a "thermofahren" or a thermo"reaumur". It's a metric's, metric's world. BSG Which number had the space mission that's crashed 'cause US-nerds did not not notice that their european colleagues calculated in metrics and not in feet?

Kiteman (author)BSG2009-03-09

Sorry, you're wrong there. The word "thermometer" means "heat measurer". A "meter" is a device for measuring. A "metre" is a unit of length.

headphoned (author)Kiteman2010-06-04

I hate it when people make an almost perfect correction, and then mess it up at the end: Meter is the [chiefly] American spelling for metre. Similarly, center for centre, liter for litre, etc. But yes, thermometer comes ultimately from the Greek thermos and metron, heat measurer.

Derin (author)2010-04-19

What is with science teachers, Brits and biros... Biros are exactly the definition our science teacher uses for pens.

Kiteman (author)Derin2010-04-19
woody558 (author)2009-11-08
"Nearly forty Desmonds...."
woody558 (author)2009-11-08
If you ask people, most will say that the first thermometer used the Celsius scale. It is a very common misconception.
A.C.E. (author)2009-08-11

great instructable. got to try this sometime

BSG (author)2009-03-09

For all the users of "imperial measures" in the 3rd world:

Download this nice piece of software: Numerical Chameleon, and rearange all your filthy Fahrenheits, gallons, miles, mpg, oz's etc. to international reliable standards. :-)

DL here:

Greetings from the "old world"


Poincare (author)2009-01-11

Mine doesn't work! I have a bigger container (made for dentures, my dad's a doctor) and a smaller straw but the water doesn't even show up on the straw!!

Kiteman (author)Poincare2009-01-11

The most likely problem is the seal, either around the straw or around the lid. Add a little modelling clay or hot-glue around any possible leak. The other thing is to make sure that there is enough air in the thermometer, since it is the air that is expanding and contracting to move the water.

lhubert (author)2008-09-10

I've tried straws in test tubes with and without alcohol added to the water. I've tried film canisters--same liquids. I've tried sealing the tip of the straw and leaving it unsealed. None seem to be working, even after holding in my hand and held in warm water. I'm out of troubleshooting ideas. Help!

Kiteman (author)lhubert2008-09-10
  • Use narrower tubes to emphasise the distance travelled by the same expansion. The inner tube of a ball-point pen is best.
  • Forget about alcohol - that is only used because it freezes below zero, it will evaporate from this design of thermometer.
  • Don't seal the top of the tube.
  • It is vital for the seal around the lid of the cannister, and around where the tube goes through the lid, to be utterly airtight.
  • When you put it together, try and start with liquid part-way up the tube, so you can see it.
  • Have a bigger air-gap inside the cannister - it is the air that is expanding, not the liquid. The water is just showing the movement of the air.

That do you?
X_D_3_M_1 (author)2007-10-22

i think i did this a while ago with clay clogging a straw.

Project_Nightmare (author)2007-03-07

I made one of these years ago. The only difference was that the instructions I followed said to add rubbing alcohol also

carbon (author)2007-03-01

Hmmm...(in order to get a good seal with the straw into the cap) couldn't you just crimp the end of the straw and slide it in? A little hard to describe: Suppose you are looking down through the straw from one of the ends. Push the top of the circumference of the end of the straw down so that the top inner half circumference meets with the other inner half of the circumference and forms a u shape. Push the two points of the u together. Now poke it through a small hole in the top and pull through as necessary. For those of you couldn't suffer through or understand that description, I might post pictures (made with paint ::cringe::).

Kiteman (author)carbon2007-03-02

If the fit it too tight, the straw will crimp all the way along, and wreck the seal completely. It would be better to drill the hole to the exact OD of the tube.

carbon (author)carbon2007-03-01

And now behold my awesome msPaint skeels! Or not :P

!Andrew_Modder! (author)2007-03-01

aww. i thaught it would give you the actual temp :P

T3h_Muffinator (author)2007-01-25

Sweet, I wish I had this project to do when I was a wee kid, I would have had a BLAST! ...hmmm, maybe I'll relive my childhood for just one hour.... hehehe

Danny (author)T3h_Muffinator2007-01-26

how could ypu have fun with a thermometer? what sort of childhood did you have?

crapflinger (author)Danny2007-01-26

one would assume...the same kind of childhood that the rest of the people who actually post good instructables here....the fun kind of childhood...spent OUTSIDE exploring and tinkering...not the modern kind...inside playing halo.

AGREED! So, what was your favorite science-related childhood memory?

Kiteman (author)T3h_Muffinator2007-01-27

The time an eight-foot python crapped down the back of my first science-teacher's back? (That was the science teacher that broke a metre ruler on the minister's son's backside and told rude poems during the lessons on reproduction, by the way.) Or my first proper science lesson, when my junior school teacher pumped the air out of a gallon oil-can and it imploded? Then the next week he dissected a cow's eye and handed the bits around... Or when my grammar school physics teacher accidentally shot a CO2 cylinder through a brick wall? ...and people wonder why I got into science teaching!

T3h_Muffinator (author)Kiteman2007-01-27

HAHA, you must be a pretty damn cool science teacher!

I know this sounds kind of lame, but mine was actually my first "instructable". At age 7 or 8, I forget which, I taught my entire 4th grade class, including the teacher, how to make goop with Elmer's glue, dish washing detergent, Borax, and some water. The next day 5 people brought in their goop, I felt so cool!.

OR (I almost forgot about this one) when my cousin and I blew something up for the first time (about age 8). That was the most awesome science "experiment" I ever did.

Too bad I'm not up to getting a job yet, junior year in high school is killer =(

one of my favorite "school" science things was when i made a fully functional (very small scale) wind tunnel for a 3rd or 4th grade science fair...even made little cars and planes to put in it....they school got a little concerned that i was burning burlap to make the smoke (the same way beekeepers do it) but the 4 fire extenguishers i brought with me made them feel a little better.. other than school stuff...the best things always involved fire or electricity or some explosive that i made or modified.

T3h_Muffinator (author)Danny2007-01-27

dude, watching water go up and down in a straw.... what more could you ask for?? As a kid I was always doing simple yet satisfying little science experiments. The first time I put a plastic cup full of water in the freezer and it broke the cup, I was in awe for about two days. Shows how little it takes to keep me amused ;-)

onlyocelot (author)2007-01-27

If you want to calibrate to the cold extreme, remember two things: a) anything you add to the water will change the freezing point, perhaps only by a little, perhaps enough to throw things off. b) water condenses as it cools, and then starts to expand again before it solidifies. That means that the scale, using water, isn't going to be a function (only one expansion-caused height for each temperature measured) but will become 2-valued near freezing (i.e., each height of the water near freezing will have two temperature values, on either side of the most dense point) For pure water, it's around 34degrees F! That means that water at 33 degrees F is about the same volume as water around 35 degrees F). It is quite valid, by the way, to calibrate a new thermometer with an existing one. It is how thermometers were calibrated for a long time after Fahrenheit made his first ones. It has only been since things were well-figured out that the glass can be ruled before the mercury is put in, and even then slight differences in the manufacturing process makes them only accurate to a certain amount. (This gets into the whole discussion of accuracy, repeatability and precision: this experimental thermometer has a limited precision (based on the width of the straw, the adhesion of the water to the insides of the straw, etc, a potential for good, but not excellent, repeatability, based on evaporation of the water and other variables (how much of the container at the bottom is in contact with the measured medium and how much the water in the straw is affected by the same medium...or not!) and accuracy (how well you draw the lines and number them, how accurate the standard you measure by). Each of the three can be affected by the others, as well!) All in all, a wonderfully wrought experiment and an interesting project. Suggestion, shapelock ( adheres well to plastic and can be made formable at 160degF (obtainable with hot water, although if your water heater is child-safe, some additional heating is needed). It should make a great seal with the straw! (Check out their free offer, too.) Shapelock is something I can't do without on the optical bench, btw: I have no commercial connection to them at all.

Kiteman (author)onlyocelot2007-01-27

Is shapelock the same stuff as "Polymorph"?

onlyocelot (author)Kiteman2007-01-28

Looks like polymorph is identical to shapelock. Shapelock folk are remarkably short on 'real information' while the Polymorph folk have a PDF that gives the chemical name and identifies the commercial title of their material. The temperatures quoted are nearly identical, and frankly, Polymorph provides a lot of really useful info like what happens if you overheat it. Looks like Polymorph is less expensive and is available in larger quantities, but apparently only in the UK?

Kiteman (author)onlyocelot2007-01-28

Not a clue, to be honest. I'm sure a quick email would reveal whether they can supply "foreign parts". Maybe there's a licensing limit?

trebuchet03 (author)2007-01-25

Cool :) You can probably get better resolution if you use a lighter than water fluid... my mind is drawing a blank at the moment, but that should work :)

_soapy_ (author)trebuchet032007-01-26

Hmm... Lighter fluid? Lighter fluid! Might have evaporation issues, though, as well as getting high. A better way might be to use a thinner straw, as you will see more expansion rate-of-change that way.

Kiteman (author)_soapy_2007-01-26

Thinner straws do work better, which is why I put biro tube in the text. Unfortunately, my science clubbers were too impatient to wait for 20 empty biros...

zachninme (author)Kiteman2007-01-26

Hmm... What about something like a chopstick stuck down the tube to make the volume smaller?

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