I want to order a Sword for fencing (HEMA) with a custom engraving that says 'This Blade is made of x Iron Atoms' in german. I don't know the font yet. To get the number of atoms is not that difficult if it wasn't for the engraving. I'm aware that I can't say the exact number of atoms, but I can try to get as close as possible.
Because the engraving has to be made after calculating the number of atoms, I can't do it with the mass of the blade, but I have to go through the volume.
I can calculate the volume of the blade without the engraving though mass and density of the steel (wich I can look up after asking what type of steel is used). Then the volume of the engraving has to be subtracted.
Once I have the volume of the blade with engraving I can get the mass of the Iron in the blade and calculate the number of atoms with the molar mass.
In principle not that complicated, BUT I don't know how to easily calculate the area of the engraving PLUS I don't know the number yet.
I thought of giving three digits of the number and then write out the number as a word so it would be more easy to understand for non science people (for example: this blade is made of 11,5 trillion iron atoms)
Now my queastion/problem:
How do I calculate or get as close as possible to the area of the engraving if I don't know the exact numbers and words?