Text file: HTML code that ive commented most of it, save it as a .HTML file to open it in the browser.
Executable: Not uploaded due to TVerse not allowing this format. Instructions are at the end on how to make it.
PS1: Powershell script that can be edited with a text editor, looks cool, no frills.
STL: Only there so this thing gets published, just a placeholder.
PDF: 4x Grey dots and faint yellow on the LH RHC of an A4 page, for 10cm and 4in, as a test print before you print the real doc to not waste a page.

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Often I find I need to resize a second print that I find doesn't quite match in size to where it is going.
Say for example I have a functional print that I want glued onto a real life object, and once I print a test print I find its a little off in one or more axis.
This could be for various reasons,
Printer E steps aren't calibrated
My initial measurements were off
I CBA to redesign it in CAD
Im looking for the PERFECT fitment

So what you would normally need to do is some math,
Which involves finding the absolute difference between two values,
Calculating the average,
Divide the absolute difference by the average,
Multiply it by 100 for the percentage difference.
Like, |x-y|/(x+y/2)x100

I couldn't be arsed with that every time.
So I wrote a powershell script that you can use and it walks you thru the process and gives it to you how you need.

1. The script will prompt you to enter the two measurements (in mm).
2. After entering both measurements, the script will calculate the percentage difference.
3. The script will then prompt you to enter your current scaling value %/mm (X, Y or Z).
4. Based on the result, it will calculate and display the new scaling percentage to apply.

Once you correct it in your slicer, you can hit R to reload for the next axis or any other key to quit.

The use case I had to spur this off was I printed a part for a chair, it was a little too short for what I needed so
I printed an addition to glue on, but for some reason my scaling settings in Cura was altered (probably from another print job still open)
Well thankfully I have the scaling values in Cura still that I can use, as it is what I just printed prior.
So I can just use this tool, to find what I have, what I need, find the scale value in Cura to alter
The resulting print is of the perfect size to seamlessly fit to the original part.

Another use case was I needed to make a bracket to fit onto a roll cage, so I made my measurements but the roll cage is not a perfectly sized tubing
So I printed a quick draft print to see the fitment and security. The next day I tried again as it was loose, I know my draft print was 100% scale
So I just needed to scale it down a smidge but I only have my measurements in mm and I needed to know the % value.
Once I worked it out, success, it wasn't going anywhere!

Thru more testing I needed this tool again,
I have a garden hose that keeps popping off, and the QD coupling needs a spacer to fit in on both ends of the hose, but each coupling has a different sized gap to fill and prevent the explosion of water, so I design one part and export to cura, printed off one spacer and fits like a glove on one end of the hose, I take a measurement of the second coupling and it is 0.7mm smaller in the Z axis, well in cura it is 6.7mm @ 100% on the Z axis currently but all other dimensions are the same, if I just change the Z measurement to 6mm the difference is 89.55% from within cura, which would've been far too large, as using the tool gave 88.98% which fit better than curas 89.55%. That might have read confusing, BUT in essence this tool provides perfect fitment for that satisfying feeling.

I realise that on some computers it might not work or they dont have the permissions on a work pc to run powershell scripts, so I included instrucitons how to make an EXE at the end.
Also I made a quick white label website that you can keep on your local machine, HTML, CSS, and JavaScript all in one file, you can edit however you like,
I will take any suggestions going forward, if you want any feature added for expansions or higher quality WHATEVER
Just make a comment and ill look to implement it if it has added value.

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(Added: June 2025)
V2.1
I have added another tool to the website only,
It offers the same capability but aimed at 2D versions, yes its mostly the same but it now provides support for px inc DPI measurements, so from 2D digital to 2D physical. Also since the calculations are different the coding is simpler this way.
Reason for this solution is this problem:
I took a photo with my phone (2D) and sent it to my pc for further designing or editing, well it almost always isn't going to be true to scale. So if the image has something of a known dimension in it, say, a ruler, then everything else on that plane will be of a known dimension and can be scaled accordingly in whatever editing program you have.

There is a use case also, to have a document on PC or MAC, which has a known dimension in it, say 4inch, you print off a test page using whatever print settings you want to use (just keep it consistent). On the test print you measure and see its at 4.25inch, well punch those numbers in the calc and hey presto, scale by 106.25%

You can also calculate between pixel, point, mm, cm and inch. To mm, cm, in, foot.
Thats a total of 20 different combinations!

28/06/2025
I have added 4x PDF pages as a test print before you print out the real deal, there are two types, grey and yellow, and of each 10cm variation and 4inch. So you get variety for your typical measurement scale, and colour.
Reason for the grey is it is easier to see and hopefully doesn't matter much in your final print (think, architectural presentations)
And for when it does matter and will be seen, the yellow can be used as will barely be noticable to the eye, but it still will show up if it is subsequently scanned.
So, print out a test page (e.g. A4 10cm Yellow LR.pdf @ 100% scale
-> measure with something
-> Input values into website calculator
-> Print out your material with the new given values.
-> Profit!

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Now a word of extra info, DPI.
If you are converting from PX to anything else, you need to know your printers specific DPI value, this, afaik can only be told from doing a test print first from a known dimension, measuring it, and dividing those two values.
Quick Math:
Effective DPI = Intended DPI × (Expected Length / Measured Length)
Intended DPI is found however you can,
Viewing a photo, right click it and go to details.
In Photoshop, Image -> Image Size -> Resolution = xxx DPI
In Illustrator, Effect -> Document raster effect settings...
In Acrobat, Print... -> Advanced -> xxx DPI

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Quick tip how to make an Executable from a ps1 file, go to:
https://www.powershellgallery.com/packages/ps2exe/
Download the latest version,
Install it, open the "Win-PS2EXE.exe" file,
Locate the ps1 file you want to convert,
Set a location for where you want the EXE saved,
Uncheck the -noConsole option,
Click Compile button.
Enjoy!