How To Scale 3D Models With No Experience

Every slicer has a Scale tool: type a percentage or the size you want in millimeters, keep “uniform” switched on, and the model grows or shrinks evenly. If a file lands in your slicer tiny, it was saved in inches; scale it 2540% and it’s right. And if you have no slicer, no printer and no software, the box below resizes an STL in your browser. One warning before you start: walls and screw holes scale with the model and nozzles don’t, so past about a third bigger or smaller you’re redesigning, not resizing. We cover that too.

Resize an STL in your browser

Drop in a file, choose a percentage or the longest side you need, download the result. The file never leaves your computer; this is the same check and rescale our upload page runs, running in your browser instead of ours.

Resized and ready? Have one of our makers print it at exactly that size, no printer needed. Instant quote, shipped to your door.

Which route is yours?

Three things that don’t scale

Scaling multiplies every dimension by the same number. The printer does not scale with it. That is where scaled prints go wrong, and it is the part most guides skip.

Walls

A 0.4 mm nozzle lays down lines about 0.4 mm wide, so a wall needs to be at least two lines thick, 0.8 mm, to print cleanly. Shrink a model with 0.8 mm walls to 50% and the walls are 0.4 mm: one line, or nothing at all if the slicer decides the gap is too thin. Fine lettering, thin fins and small pegs disappear first. Going up is kinder: a 0.8 mm wall at 200% is 1.6 mm, which prints better than the original.

Holes for real hardware

An M3 screw is 3 mm whatever size the print is. A 608 bearing is 22 mm across. A AA battery, a phone, a magnet, a Raspberry Pi: none of them shrink when you scale the case. Scale a part with hardware holes and every one of them is now wrong. The fix is to resize the body and put the holes back to their real size, which means editing the model, not scaling it.

Tolerances

A well-tuned printer is accurate to roughly ±0.2 to 0.3 mm, at any size. Designers leave about that much clearance in snap fits, threads, lids and pegs. Scale a part down and those clearances close up and jam; scale it up and they go sloppy. Threads are the worst case: pitch and depth scale together and stop matching any real screw.

Rule of thumb: a decorative model scales as far as you like, within the wall limit above. A part that has to fit something else should be edited to the new size, not scaled. If that’s beyond what you want to learn, send the file to a 3D design engineer: describe what it has to fit, and they resize the body and keep the holes and clearances right. The chat is free; you only pay if you order the work.

Scale it in your slicer

Same job in every slicer: select the model, open Scale, keep uniform on, type a percentage or a size.

Bambu Studio and OrcaSlicer

Click the model, then the Scale icon in the top toolbar. The panel shows Scale (%) and Size (mm) for X, Y and Z with a “Uniform Scale” checkbox. Leave it checked, type a percentage in any box or the size you need in one of the mm fields, and the other two follow. Uncheck it only when you want to stretch one axis, for instance making a lid 1 mm taller without widening it. Both slicers notice a model that imports very small and ask whether it was saved in inches; say yes and they multiply by 25.4. One caution from Bambu Studio’s 2.8.4 beta: it applied that conversion silently to small sub-parts of multi-part files, so if a part in an assembly suddenly grew 2540%, that is why. Check the Size fields after any import.

PrusaSlicer

Select the model and press S. Drag a corner box to scale uniformly, or an axis handle for one direction (hold Ctrl for an asymmetric stretch). Hold Shift for 5% steps. The panel on the right takes exact mm or percentages. Two shortcuts worth knowing: with Scale open, F scales the model to the maximum size your printer can fit; and the Measure tool (PrusaSlicer 2.6 and later) lets you click a measured distance and type what it should be, which scales the whole model to match. If a file imports tiny, PrusaSlicer asks whether to convert from inches, and you can do it later from the right-click menu.

Cura

Select the model and click the Scale tool in the left toolbar. You get mm and percentage fields for each axis, a “Uniform Scaling” checkbox (keep it on) and “Snap Scaling”, which moves in 10% steps when you drag. Holding Ctrl while dragging temporarily unlocks uniform scaling. Cura has no inch prompt; type 2540 in a percentage field. Under Preferences, “Scale large models” and “Scale extremely small models” resize files automatically when you open them, which is handy until it quietly changes a part you wanted at its real size. We’d leave both off.

Blender

Overkill for a resize, but if you’re already in it: press N, open the Item tab, and type real sizes into the Dimensions fields rather than fiddling with Scale. Then Ctrl+A and Apply Scale before exporting, or the STL goes out at the old size. Blender’s scene unit is meters by default; the STL exporter has a scale setting, so check the export in your slicer.

Microsoft 3D Builder, which a lot of older guides recommend, was pulled from the Microsoft Store in 2024. Don’t go looking for it; any slicer above does the job.

No printer, no software: Tinkercad

Tinkercad is Autodesk’s free, browser-based modeling tool and the easiest way to resize a file if you have no slicer installed. The box at the top of this page is faster for a plain resize; use Tinkercad when you also want to change the model, add text, or cut it. There’s a video walkthrough on this page too.

Sign in at tinkercad.com, click Create, then 3D Design.

Click Import (top right). Tinkercad takes STL and OBJ files up to 25 MB. Before the model loads you can set the scale and units, so if you already know it needs to be 150% or that it was saved in inches, do it here.

Click the model. White corner handles resize it; hold Shift while you drag a corner to keep the proportions. The numbers next to the handles are the size in millimeters, and you can click one and type an exact value. The single handle on top changes the height.

Export, choose .STL, and the resized file downloads. Very detailed scans can exceed what Tinkercad will import; for those, use the box at the top of this page, which has no triangle limit, or your slicer.

Then upload the STL for an instant quote. Our makers print it at the size in the file and ship it to you.

Why your model came in tiny: the inch problem

An STL file has no units. It is a list of triangle corners with plain numbers, and every slicer reads those numbers as millimeters. Save a model from software set to inches and a 2-inch part arrives as a 2 mm part, 25.4 times too small. It happens to everyone once.

It happens to our customers too. One upload arrived at 0.394 × 0.394 × 0.025 mm: a 1-inch square tile, saved in inches. The thickness came out thinner than a single print layer, so the slicer produced nothing and the quote silently failed. We built a check for it after that. Today the upload page measures every STL before quoting: if a part is thinner than a layer or smaller than a couple of millimeters, you get a card that says what size it is and offers to scale it, with the likely unit (inches, centimeters or meters) already worked out. The corrected file is what gets stored, so the maker prints the right size. Models that are too big for the build volume get a “Scale to fit” offer the same way. A normal-size model gets no prompt at all: we print the file at the size it is in, so set the size before you upload or use the box at the top of this page.

The fix in any slicer is 2540%. In Bambu Studio, Orca and PrusaSlicer you’ll usually be asked on import. In Cura or Tinkercad, type it. And if the model is 10 times too small rather than 25.4, it was saved in centimeters: 1000%.

Scale to a real measurement

Most resizing jobs are “make this fit that”: a lid for a jar, a holder for a bottle, a bracket for a shelf. The order of operations matters.

• Measure the real thing with calipers, not a tape measure. We keep a Sangabery digital caliper on the bench; it switches between inches and millimeters with one button and reads to 0.1 mm, which is plenty for printing. The NEIKO 01407A is the other common pick and reads to 0.01 mm.
• Pick the one dimension that has to be right (the inside diameter of the lid, the width of the slot) and scale off that. In the box above, type that dimension as the longest side if it is the longest side; otherwise work out the percentage: needed ÷ current × 100.
• Add clearance instead of scaling for fit. A part that should slide over something needs about 0.2 to 0.4 mm extra; a press fit needs about 0.1 mm less. Scaling the whole model to add 0.3 mm to a hole also changes every wall. If the clearance is the only thing wrong, edit the hole.
• Test-print a slice. Cut the model down to the 5 mm that matters (every slicer can cut) and print that first. Ten minutes beats a failed 6-hour print.

If the part has several things to fit, or threads, or it has to be strong, this is where a design engineer earns their keep: send the file and the measurements and get back a model sized to fit.

Scale models and miniatures

To move a model between scales, divide the old scale’s denominator by the new one: 1:10 to 1:6 is 10 ÷ 6 = 166.7%. 1:48 to 1:87 is 48 ÷ 87 = 55.2%. Common scales:

Remember the wall rule: an HO building that was drawn for 1:48 has walls half as thick after the conversion, and window mullions often vanish. Check the thin parts in the slicer preview before printing.

Scaling up: time, material and your build volume

Size scales in three directions at once. Double the size and the volume is eight times larger, so expect roughly eight times the filament and something like eight times the print time (see how long 3D printing takes). Overhang angles stay the same, but bridges get longer and big flat bases warp more, so a part that printed fine at 100% can need a brim and a slower first layer at 200%.

Most desktop printers stop at about 220 to 256 mm per side. Past that, either split the model in the slicer and glue the pieces, or send it to a bigger machine. We run a large-format printer with a 420 mm bed alongside our Bambu machines for exactly this, and the maker network has more. Upload the model and the quote tells you straight away whether it fits.

FAQ

How do I resize an STL file online?

Use the box at the top of this page. Drop the STL in, type a percentage or the longest side in millimeters, download the resized file. It runs in your browser and never uploads the file.

How do I make a 3D print smaller?

Select the model in your slicer, open Scale, keep uniform on and type a percentage under 100. Check that the thinnest walls are still at least 0.8 mm (two lines of a 0.4 mm nozzle) in the preview before you print.

How do I scale an STL to an exact size?

Type the size you need in one of the mm fields with uniform scaling on; the other two axes follow. In the box above, type it as the longest side.

Why is my model tiny in the slicer?

It was saved in inches. STL files have no units and slicers read them as millimeters, so everything comes in 25.4 times too small. Scale it 2540%, or say yes when the slicer asks whether to convert from inches.

Can I scale just one axis?

Yes: turn uniform scaling off and change X, Y or Z alone. Round holes become ovals and angled surfaces change angle, so keep it for things like making a box taller.

Does scaling a model change print time?

Yes, by the cube. 150% size is about 3.4 times the material and time; 50% is about one eighth.

What percentage is 1:48 to 1:87?

48 divided by 87, so 55.2%. Divide the old denominator by the new one.

Will Intagly print my model at the size I set?

Yes. The upload is quoted and printed at the size in the file. If the file looks like a unit mistake or is too big for the build volume, the upload page says so and offers a one-click fix before you order.

Recap

No printer? Upload the resized STL and one of our makers prints it at that size and ships it to you.