Scientific Calculator
Type the whole sum and see it as you go. The angle mode is on screen rather than hidden behind a button, because that is where most wrong answers come from.
Degrees or radians, said out loud
This is where nearly every wrong trigonometry answer comes from, and
on a pocket calculator the mode is a tiny letter in the corner that
nobody looks at. Here it is a dropdown with the answer written into
it: sin(30) is 0.5 in degrees and
-0.988 in radians. Both are correct. Only one is
what you meant.
School geometry, surveying and most engineering are in degrees. Anything that came out of a programming language or a physics formula is almost certainly radians.
Why 0.1 + 0.2 is not quite 0.3
Type it in and the exactness tile will say rounded. The machine's answer is 0.30000000000000004, and it is not a bug.
Computers store numbers in binary, and a third of the everyday decimals cannot be written exactly in binary any more than a third can be written exactly as a decimal. 0.1 is stored as something almost exactly a tenth, 0.2 likewise, and the two almosts add up to a visible speck. Every calculator on every computer has this; most hide it by rounding the display and saying nothing.
This one rounds the display too — twelve significant figures, which is where the noise starts — but it tells you when it has done so, and the tick box shows you everything the machine actually holds. That matters if you are chasing a discrepancy in a spreadsheet: now you know where it came from.
It reads the sum rather than running it
There is a short cut for building a calculator on a web page: hand what the visitor typed to the browser and let it run as code. It is a few lines and it is an open door — whatever is in that box gets executed.
So this reads the expression properly instead: splits it into numbers, operators and function names, arranges them by precedence, and works out the answer. Nothing you type is ever run as code. The practical upshot is that a typing mistake gives you a message about the mistake, rather than a strange result from something you never meant to write.
The small print of the keypad
log is base 10 and ln is natural, which is
the usual convention and is worth checking on any calculator you did
not write. % is the remainder after division, not a
percentage — for percentages use plain arithmetic.
! is factorial and only for whole numbers up to 170,
after which the answer is larger than the machine can hold.
2(3+4) works and means what it looks like.
Frequently asked questions
sin(30) gives a strange number. Why?
The angle mode is on radians. In radians 30 is about five full turns and a bit, and the sine of that is -0.988. Switch the dropdown to degrees for 0.5. This is the single most common mistake with any calculator.
Why does 0.1 + 0.2 not give exactly 0.3?
Because binary cannot write a tenth exactly, just as decimal cannot write a third exactly. The tiny error is real and is in every computer. The page tells you when it has rounded the display rather than pretending otherwise.
Is log base 10 or base e?
log is base 10 here and ln is base e, which is the common convention. It is worth checking on any calculator, because a few use log for the natural logarithm and the two differ by a factor of about 2.3.
What does the % key do?
The remainder after division - 7 % 3 is 1. It is not a percentage key. For a percentage, divide: 15% of 80 is 80 * 15 / 100.
Can I use it for very large numbers?
Up to about 15 or 16 significant digits exactly, after which digits start to be approximate - that is the limit of the number format, not of this page. Factorials stop being exact at 21! and overflow entirely past 170!.
Is my text sent anywhere?
No. Everything happens in JavaScript inside your own browser. Nothing is uploaded and nothing is saved - close the tab and it is gone.