Yeah, I also don't understand what exactly it is, that you are asking.
In Blender a Unit corresponds to a Meter, which makes sense, when you want to model both large (eg buildings0 and small (eg bugs) things.
For 3D printing, having a Meter as Unit, would be quite inconvenient.
hi, sorry my question wasn´t very clear, i ask 2 diferent thing so, the first one if is posible to make match the units because when i export something as a stl file from blender, the objects are 100 times smaller (like 1 meter in blender = 1 milimeter in a STL 3d printable file), and the second i don´t have it very clear what i was asking hahaha, sorry and that for your patience.
What you need to do is keep everything in meters, but make blender show the meters as if they are millimeters. Here's how to do it.
Go to properties editor->Scene tab->units panel
1. Change length to Millimeters. This makes the units in blender show as millimeters.
2. Then change scale to 0.001. This makes moving or scaling 1 MM actually moves/scales 1 meter.
3. In the 3D viewport, click the overlay drop down arrow in the header and change the scale to 0.001. This makes the grid match with the scale setting under units.
You can also just convert them and scale the model to fit the size you want like Porter does in the first lesson of this course: