3D Model Scale & Bed Fit Calculator
Enter the model's size and either a scale, a target dimension or the printer you want it to fit. Get the new dimensions, whether it fits (including rotated), and how the volume — and therefore print time and filament — changes.
The formulas
new dimension = current × scale
volume factor = scale³ (also filament and, roughly, print time)
largest scale that fits = min(bed X ÷ model X, bed Y ÷ model Y, height ÷ model Z), tried both ways round
Worked example
A 120 × 80 × 150 mm figure should be 100 mm tall.
- Scale: 100 ÷ 150 = 66.67%
- New size: 80 × 53.3 × 100 mm
- Volume: 0.6667³ = 29.6% of the original — a print that took 10 hours now takes about 3
The same figure at 200% would be 240 × 160 × 300 mm and need eight times the filament. That's usually the moment people discover it doesn't fit the printer, which is what the fit mode is for.
Three ways to scale in the slicer
Every mainstream slicer (PrusaSlicer, OrcaSlicer, Bambu Studio, Cura) has an object panel with a percentage box and three size boxes, and a padlock or "uniform" toggle. With uniform scaling on, typing either the percentage or a target size in one axis scales all three; the calculator's output is what to type. Turn uniform scaling off only when you deliberately want to stretch one axis — for instance, making a box taller without widening it, or applying different shrinkage compensation to Z than XY.
Fitting the bed
Bed presets are the manufacturer's nominal build volumes. Two things reduce what you can actually use:
- The margin. A brim adds 5–8 mm all round; a skirt a couple of millimeters; glass clips or a purge line can steal a strip along one edge. The default 5 mm margin is a sensible minimum; use 8–10 if you print with brims.
- The corners. Some printers (notably Bambu machines) reserve a corner for the purge/wipe area, and many bedslingers can't reach the last few millimeters at the back. If a print is within a few percent of the limit, check the slicer's actual bed outline.
The calculator checks the footprint as-is and rotated 90°, and gives the largest uniform scale that fits when neither works. It doesn't try diagonal placement: a long thin part can often go corner-to-corner (the diagonal of a 220 mm bed is 311 mm), so if the rotated check fails narrowly, try 45° in the slicer.
Things that don't survive scaling
Scaling a model scales everything in it, including the features you'd rather stayed put. Walls thinner than two extrusion widths (about 0.9 mm with a 0.4 mm nozzle) print badly or not at all; scaling a model with 2 mm walls below 45% gets you there. Holes for screws and bearings, snap-fit clearances and threads all change size — a model designed for M3 screws scaled to 80% wants M2.5. Text and fine details below about 0.5 mm vanish. When a scaled part must fit real hardware, it's better to open the model and resize the body while leaving the holes alone, or to scale and then use the hole compensation to bring the holes back.
Unit mix-ups
STL files carry no units. A model designed in inches and opened by a slicer that assumes millimeters comes in 25.4 times too small; the reverse comes in 25.4 times too large. If a model imports as a speck or a monolith, that's almost always what happened, and the fix is exactly a 2540% or 3.937% scale — the calculator flags it when the factor matches. 3MF and STEP files include units and don't have this problem.
Frequently asked questions
How do I scale a model to a specific size?
Divide the size you want by the size it is. A 120 mm model that should be 90 mm needs 90 ÷ 120 = 0.75, or 75%. Apply that uniformly to all three axes in the slicer's scale box, or type the target directly into the axis field — every mainstream slicer scales the others to match when uniform scaling is locked.
Why does scaling to 50% cut the weight to an eighth?
Volume scales with the cube of the linear scale. Half the size in every direction is ½ × ½ × ½ = ⅛ the volume, so roughly an eighth the filament and print time. Doubling a model uses eight times the material — the calculator shows this factor so it doesn't surprise you.
My STL imports tiny or huge. What scale fixes it?
The file was saved in inches or the slicer assumed the wrong unit: STL has no units. If it's 25.4× too small, scale by 2540%; if 25.4× too big, scale by 3.937%. Most slicers have a 'convert from inches' option that does the same thing.
Will a model fit if I rotate it?
Often. The calculator checks the footprint both ways round — a 250 × 200 mm part doesn't fit a 220 × 220 bed as-is but does on a 250 × 210 Prusa bed either way, and a long thin part can fit diagonally. It also gives the largest uniform scale that fits when it doesn't.
Does scaling affect wall thickness and tolerances?
Yes. Walls, pins, holes and clearances all scale with the model. A 2 mm wall at 50% becomes 1 mm, which may be thinner than two extrusion lines; a 5 mm hole becomes 2.5 mm. Check fits after scaling, and use the shrinkage calculator for material compensation, which is a separate, much smaller adjustment.
Last reviewed September 7, 2026. Spotted an error or want another calculator? Tell us.