Resize any STL between miniature scales, calculate model dimensions from real measurements, or determine an unknown STL's scale. All calculations run instantly in your browser.
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Resize an STL to another scale
More scales
More scales
Any number works — type 87.1, 22.5 or 33.5 if that is what you need.
Resize your STL to
1:87 → 1:48
Enlarge by 81.25%
Show calculation
87 ÷ 48 = 1.8125
Multiplier — enlarge
Existing scale ÷ desired scale × 100 = the percentage. Scale X, Y and Z by the same number.
I don't know the model's scale — size it from a real-world measurement instead
Measure one dimension of the STL as your slicer reports it, say what that dimension is in real life, and pick the scale you want.
Convert real dimensions to model size
Enter the real-world dimensions of the thing you are modelling and the scale you build in. Results come out in millimetres and inches.
Don't know the scale? Use something you recognise.
Find something on the model whose real size you know — a door, a person, a railroad gauge — measure it on the model, and the ratio between the two is the scale.
Example: 80 in real door → 23.36 mm STL door → approximately 1:87 · Closest common scale: HO
A reference measurement is only as good as the reference. If you know the actual prototype dimension — the real locomotive, the real building — use that and the answer is exact. Everyday sizes like the 80 in door are a useful estimate for a lot of US residential work, but they are not universal: doors vary by country, by age of building and by use, and figures are often sculpted taller than life. Nothing here is rounded to a standard scale for you.
Estimate dimensions from a photo
Measure something you know in the photo in pixels, measure the whole building in pixels, and the known height gives you the rest.
Photos lie about size. A camera makes anything closer to the lens look larger, so pick a reference on the same face of the building, at the same distance from the camera, and shot as square-on as you can find. A door photographed from the side of a building can be out by 20% or more.
How to determine the scale of an STL file
Four methods
Method 1 — a measurement you already know
If you know any real-world dimension of the subject, measure the same dimension on the model and divide. A locomotive that is 50 ft long in reality and 175 mm long as imported is 15240 ÷ 175 ≈ 1:87. This is the most reliable method there is, and it is the only one that gives an exact answer.
Method 2 — reference objects
When you have no spec sheet, borrow a size from something ordinary in the model:
- Residential door — about 80 in (6 ft 8 in) tall
- Doorway — about 30 to 36 in wide
- Adult human — about 69 in, though figures are sculpted taller than average
- Car or truck wheelbase, when you can identify the vehicle
- Standard railroad gauge — 56.5 in between the rail heads
- Shipping container — 20 or 40 ft long, 8 ft wide, 8 ft 6 in tall
- Dimensional lumber — a nominal 2x4 is actually 1.5 in by 3.5 in
- Architectural bits — bricks, stair risers, window heights, handrails
These are typical sizes, not standards. Unless you know the exact prototype, the result is an estimate — a good one, but an estimate.
Method 3 — the maker's own numbers
Product pages, README files and the model's own filename often state the scale or a printed size. Every Miniature Reality listing states the scale it was cut for.
Method 4 — compare against a model you trust
Put the unknown model next to something you know is right. If your HO figures stand level with the door handle instead of below the lintel, the building is not HO.
The formulas
All seven
- New scale %
existing scale ÷ desired scale × 100 - Model size
real size ÷ scale - Real size
model size × scale - Scale
real size ÷ model size - Resize %
desired model size ÷ current STL size × 100 - Inches to mm
inches × 25.4 - mm to inches
mm ÷ 25.4
Both sides of a division have to be in the same units before you divide.
Common scales at a glance
One real measurement, every common scale — and a quick word on whether your printer can handle it. Handy to print and pin above the bench.
| Scale | Model size (mm) | Model size (in) | Prints on? |
|---|
Swipe the table sideways for the “Prints on?” column. Based on a typical 220 mm FDM bed and 150 mm resin plate; bigger parts can be split or tilted, and dedicated large-format machines go further.
Common scale notes
HO, O, N, G, and 28mm
- HO is 1:87.1 exactly. Almost everyone writes 1:87, and either number lands within a tenth of a percent.
- O scale is 1:48 in the US, about 1:43.5 in Britain, about 1:45 in Europe.
- N scale is 1:160 in the US and Europe, about 1:148 in Britain.
- G is a family of garden-railway scales rather than one ratio — 1:22.5 is the common one, but 1:20.3, 1:24 and 1:29 all get called G.
- 28mm and 32mm gaming figures are sizes, not scales. Different makers measure to the eyes, the top of the head, or the top of the hat, so a "28mm" range can work out anywhere from roughly 1:56 to 1:64. Measure a figure you own and use the identify tool above.
Scaling an STL in your slicer
Where the scale field lives
An STL file carries no units and no scale. It is a mesh of numbers, and the slicer decides those numbers are millimetres. That is why the same file prints at the right size for one person and comes out doll-sized for another — the geometry never changed, the interpretation did.
Scale X, Y and Z by the same percentage unless you deliberately want a distorted model. Every slicer has a uniform or lock-aspect toggle; leave it on.
- Lychee Slicer — scale field in the right-hand object properties panel.
- Chitubox — the Scale tool on the left toolbar, with a lock for uniform scaling.
- PrusaSlicer — the object manipulation panel on the right; type a percentage or a target size.
- Bambu Studio — the Scale tool in the left toolbar, same panel on the right.
- Cura — the Scale tool on the left; percentages and millimetres both work, with Uniform Scaling ticked.
Two things to keep an eye on after a big reduction: wall thicknesses that drop below what your printer can resolve, and small details that vanish. Scaling up is safer, but check the model still fits the build plate.
Where these numbers get used
- Model railroading — HO at 1:87.1, N at 1:160, O at 1:48, TT at 1:120.
- Dioramas — 1:35 military, 1:24 vehicles, and whatever the scene needs.
- Wargaming — terrain for 28mm and 32mm figures, usually around 1:56.
- Dollhouses — 1:12 for the classic one-inch scale, 1:24 for half-inch.
- Fantasy tabletop — figure-scale scenery, sized to the minis on your table.
Files in the shop are $2.99 and state the scale they were cut for. If the scale you need is not the one listed, the calculator at the top of this page gives you the slicer percentage to get there.
Questions people ask
What percentage do I use to go from 1:87 to 1:48?
181.25%. Divide the scale you have by the scale you want and multiply by 100: 87 ÷ 48 × 100 = 181.25. Apply it to X, Y and Z together.
How do I work out what scale an STL is?
Measure something on the model whose real size you know — a door is about 80 in tall — and divide the real size by the model size in the same units. 2032 mm ÷ 23.36 mm is about 87, so the model is about 1:87.
Does an STL file have a scale built in?
No. An STL is just numbers describing a mesh, with no units attached. Your slicer assumes those numbers are millimetres. That is why the same file prints correctly for one person and doll-sized for another.
Is HO 1:87 or 1:87.1?
Both, in practice. The standard is 1:87.1; almost everyone writes 1:87. The difference is about a tenth of a percent — far less than printer tolerance — so either number is fine here.
Will scaling down ruin a pre-supported resin model?
It can. Supports scale with the model, so contact points, shafts, wall thickness, hollowing and drain holes all shrink too. After a substantial reduction, check the supports or rebuild them.
Can I use a scale that isn't a standard one?
Yes. Type any number — 33.5, 87.1, 22.5 — and the maths works the same. The page tells you the nearest common scale for reference, but it never rounds your number to it.
Printable scale reference
The formulas and the conversions worth keeping on the wall. Save it, print it, pin it.
