Convert G-code to STL

What you get back, and what you do not

The original model is not inside a G-code file. A slicer cut it into layers, turned each layer into paths for the nozzle, and threw the model away. No converter anywhere can get it back, because it is not there to get.

What is there is every move that pushed out plastic, and how much plastic each move pushed. That is enough to rebuild the print itself. Each line becomes a strand with a width and a height, and the strands stacked up are the object that would come off the bed.

So the result is stepped, like the print. Every layer shows, and a curved top is a staircase of 0.2 mm steps. Anything the slicer changed on purpose — a hole made slightly bigger, a first layer pulled in so it does not spread — is in the result, because it was in the print.

Why the file is much bigger than the model was

A model describes a surface. A rebuilt print describes every line of plastic separately, and a print has tens of thousands of lines. Each one becomes a small closed tube that overlaps its neighbours, which is how plastic is really laid down. It is also why a 2 MB model, sliced and rebuilt, can come back as a 60 MB STL.

Two settings keep this under control. "The part only" leaves out infill, supports, the skirt and any prime tower, which usually cuts the file to a third and leaves the outside of the part exactly as it was. "Fast" gives every line a square cross-section and simplifies curves to within a third of a line width, which you cannot see at print scale.

If a print is too large to rebuild in a browser tab at the settings you chose, the tool steps down on its own — accurate to fast, then everything to the part only — and says which step it took.

When this is useful

You have a G-code file and nothing else: a print someone shared, a job from a print farm, a file from years ago whose model is lost. The rebuilt STL is something you can look at, measure, and put next to other parts in CAD to check a fit.

You want to show what a print will really look like, layers and all, rather than the smooth model it came from.

You want to print it again on a different printer. Slicing the rebuilt STL again is much safer than running G-code made for somebody else’s machine, which can drive the nozzle into the bed. Expect the old layer lines to show on the new print; for a functional part that is usually fine.

When it is not the right tool

If you still have the model, use the model. An STL sliced from a real model is smooth and small; one rebuilt from G-code will always be stepped and large.

If you only want to look at the print or check it before you start it, the G-code viewer is the better page. It draws the lines directly, layer by layer, and tells you the print time and the filament without building anything.

Binary G-code (.bgcode), which PrusaSlicer writes for its newer printers, cannot be read yet. PrusaSlicer writes plain G-code for the same printer if you untick one setting, and the message you get says which.

Units and position

G-code states its units: G21 means millimetres and G20 means inches, and inches are converted. The model comes out in the printer’s own coordinates, Z up, sitting exactly where it sat on the bed. Several parts from one plate therefore stay where they were relative to each other.

If you want the part at the origin instead, move it in your slicer or CAD program after converting. Nothing about its shape changes when you do.