AutoCAD Scale Factor: 1:100 to 1:50
A scale factor answers how much a represented length changes between two scales. Before entering a SCALE factor, decide whether you are changing an already scaled drawing object or only changing how a full-size model appears on paper.
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Concepts
What 1:n represents
With matching units, 1:n means one paper length represents n real lengths. At 1:1 the lengths match; at 1:10, 1:50 and 1:100 the same real object occupies progressively less paper length. The denominator is not the enlargement factor itself.
Changing from one scale to another
For the same real object and the same representation units, the required length factor is old denominator divided by new denominator. Changing 1:100 to 1:50 doubles the represented length; the reverse change halves it.
Model space and paper space
AutoCAD models are normally drawn at full size in the chosen model unit. Layouts and viewports provide scaled views on a paper-space sheet. Changing a viewport scale is different from changing model geometry with SCALE; do not enlarge a correct full-size model merely to change its printed representation.
Units, annotations and plotting
A model unit may represent mm, m or another length unit. Unit conversion and scale conversion are separate operations. Dimension styles, annotative objects, linetypes, viewport settings and PDF fit-to-page options also need checking after a representation change.
Basic formulas
Scale 1:n → Lreal = Ldrawing × n Ldrawing = Lreal / n Factor = nold / nnew If units differ: Factor × unit conversion factor
- nold and nnew: dimensionless denominators of old and new 1:n representation scales.
- Ldrawing and Lreal: lengths expressed in compatible units; Factor: dimensionless length multiplier.
- When units differ, include the appropriate length-conversion factor in addition to nold/nnew.
Worked example
A 50 mm paper representation at 1:100 corresponds to a 5 m object. At 1:50 the same object occupies 100 mm, so the representation factor is 2.
1:100 → 1:50: Factor = 100 / 50 = 2 50 mm × Factor = 100 mm (paper representation) 50 mm × 100 = 5000 mm = 5 m (real length) 1:50 → 1:100: Factor = 50 / 100 = 0.5
The scale-conversion calculator returns 2 for old = 100 and new = 50. The drawing-scale calculator checks the independent relation 50 mm × 100 = 5,000 mm.
If the model already contains the true 5 m geometry, preserve it and adjust the appropriate viewport/plot presentation instead of blindly applying SCALE 2 to the model.
How to use this in practice
For imported or already scaled geometry, establish a known reference length, confirm source and destination units, then calculate and verify the required factor. Keep a copy of the drawing before geometric changes.
For output changes, check the layout, viewport scale and plot settings. Measure a known printed length in the final PDF or plot, and ensure that fit-to-page has not added another factor.
Common mistakes
- Reversing old/new gives 0.5 instead of 2 when moving from 1:100 to 1:50.
- Rescaling full-size geometry to change paper output alters the represented engineering dimensions.
- Ignoring metre-to-millimetre conversion or annotation settings can make a correct numeric factor look wrong.
Related calculators
Related guides
Frequently asked questions FAQ
Should I enter 1/100 in the old-scale field?
Enter the denominator 100 for a 1:100 scale. The calculator divides the old denominator by the new one.
Does factor 2 mean I should always SCALE the model?
No. It describes the representation change. A full-size model should usually retain its geometry while its viewport or output scale changes.
How do I check the final drawing?
Measure a known reference length and inspect the output scale and unit settings. Also review dimensions, text and linetypes because they may not follow geometry in the same way.
References
Engineering Disclaimer
Calculations and examples are references based on general formulas and stated assumptions. Before design, construction, manufacturing, inspection or approval, check applicable standards, project requirements and approved manufacturer or vessel data, and follow the required review procedures. These results do not imply certification or design approval by any authority.
Calculation disclaimer