If you just imported a model into Unreal and it arrived the size of a grain of rice, here is the whole answer before anything else: one Unreal unit is one centimeter, the tool you modeled in almost certainly works in meters, and the two disagree by exactly 100. Fix it in the import options, not in the level. In the FBX import dialog, set Import Uniform Scale to 100, or set Convert Scene Unit if your exporter wrote real units into the file, and reimport. If the model came in absurdly huge instead, the number is 0.01.
That is the fix. If it unstuck you, go build something. The rest of this is why it happens, why the scale handles sitting right there in the level are the wrong tool even though they look like the right one, and how to check any size in five seconds without importing anything again.
One unit is one centimeter
Unreal measures distance in centimeters. Epic's Units of Measurement page lists Distance/Length as Centimeters (cm), and you can see every quantity and its unit under Edit > Project Settings > Editor > Appearance, expanding Units > Advanced.
So the arithmetic is one line: 100 units is 1 meter. A 3 meter wall is 300 units. A 220 unit doorway is 2.2 meters. To read units as meters, move the decimal point two places to the left. Do not chop the last two digits off, which is the version people remember: 45 units is 0.45 meters, and chopping turns a step into no step at all.
Where the 100 comes from
Most modeling and CAD tools measure in meters. Unreal measures in centimeters. Nothing else has to go wrong for your model to arrive unusable.
A chair modeled as one unit tall means one meter in the tool and arrives as one centimeter in Unreal. You get a chair you need to zoom in to find. The mistake runs the other way too, and then a doorway lands a hundred times too big to fit on screen.
The useful part is that the factor is never 3 or 7. It is exactly 100, or exactly one hundredth going the other way. That makes this the most diagnosable problem in the whole import pipeline: if you can see a hundredfold error, you are looking at a units disagreement, not a modeling mistake, and you do not need to open the source file to know it.
The two settings, and which one to reach for
Unreal's FBX import options carry two settings that deal with this, and they are not the same tool.
Convert Scene Unit, in the Miscellaneous section, in Epic's words "will convert the scene from the FBX units of measurement to UE's unit of measure, centimeters." That is the one built for this job. It reads the unit the exporter recorded in the file and does the conversion for you, so you never type a number and never have to remember which direction you are going.
Import Uniform Scale, in the Transform section, "will enable the mesh to be scaled uniformly when imported." That is the manual override: 100 when models arrive too small, 0.01 when they arrive too big.
Reach for Convert Scene Unit first. If your exporter wrote its units honestly, that is the end of it. Plenty of pipelines do not, and that is what Import Uniform Scale is for. Either way you are correcting the import, which means the asset itself comes in at the right size, which is the thing that matters for every reason below.
Why scaling it in the level is the wrong fix
This is the part most answers skip, and it is the part that costs people a week later.
Grabbing the model in the level and dragging the scale handles until it looks right does make it look right. It also leaves the asset wrong, and the asset is what everything else reads.
Collision belongs to the mesh, not to the copy you dragged. Physics is tuned for a world measured in centimeters, so a body that is a hundred times the wrong size falls, slides and bounces wrong no matter what the level transform says it looks like. Anything you attach inherits the parent's scale, so a weapon snapped to a resized character comes along at the same wrong scale, and so do its effects and its own collision. Animation is authored against a character's real size. And the moment you place a second copy, you are applying the same fudge by hand again, forever, on every model that ever comes out of that tool.
There is a quieter cost too. Once you have a level full of objects at 100 scale, the numbers in front of you stop meaning anything. You can no longer look at a value and know what size it is, because half your objects are lying about theirs. You have traded a problem you can diagnose in one glance for one that hides.
Correct the import, not the object. It takes the same thirty seconds, and it is the version that holds.
The ruler, so you can check anything
Knowing the conversion still does not tell you whether 600 is big. What does that is a short list of sizes you already know cold, in units, to measure everything else against:
- A person: about 175 units.
- A door: about 210 units.
- A car, end to end: about 450 units.
- A generous room or a double garage: about 1000 by 1000 units.
- A tall building: 5000 units and up.
Three of those are enough. A person at 175, a car at 450, a tall building at 5000 give you a low, a middle and a high rung, and every other size sits somewhere on that ladder. A value of 300 is taller than you and about ceiling height. A value of 90 is knee to waist, a crate or a low table. A value of 5000 is a landmark.
Now the import check takes a second. Your character model should be somewhere near 175. If it reads 1.75, the file came in as meters and you already know which setting to change. If it reads 17500, you went the wrong way with the number. You never have to guess whether the model is wrong, because you have something to compare it against.
Two more symptoms out of the same file
Size is the loudest way an import can disagree with you. Two others turn up often enough to recognize on sight, and each one points at a different setting.
It arrived lying on its side. The lettering on the model still reads the right way round, nothing is mirrored, and the thing is simply not standing up. That is a coordinate system disagreement rather than a size one, and it lives in the same Miscellaneous section: Convert Scene "will convert the scene from the FBX coordinate system to use UE's coordinate system", and Force Front XAxis "will convert the scene from the FBX coordinate system to UE's coordinate system with the front X axis instead of -Y axis." Which of the two you need depends on what the exporter considered forward.
It arrived mirrored. It stands up straight and the lettering runs backwards, a character's holster is on the wrong hip, and nothing looks broken until you read the writing on it. This one is worth knowing because there is no mirror switch in Unreal's import options to flip. A mirrored model is a negative scale, baked into the source file or introduced on export, so the fix is in the tool it came from rather than in Unreal. Flipping it in the level has exactly the problem scaling it in the level has: the asset is still wrong, and the next model out of that pipeline arrives wrong the same way.
Three symptoms, three different places to look, and in all three cases the thing to correct is the import rather than the object sitting in your level.
The habit worth taking from this
The fix here is thirty seconds long. The habit is worth more: when something arrives wrong, read the symptom before you reach for the handles. A hundredfold size error is units. A model on its side with correct lettering is an axis conversion. A model standing up with backwards lettering is a mirror in the source. None of those three is a judgment call, and none of them is fixed by dragging something until it looks right.
That is the difference between using an engine and understanding one, and it is most of what separates a developer who fights Unreal from one who does not.
If you want the fact underneath this rather than the fix, we teach it as a free lesson: What the Numbers Mean: 1 Unit = 1 Centimeter, where the 100, the anchors and the three symptoms come from. It sits in a track you can take without writing a line of C++.