# Reading Drawing Scale (or Units) **URL:** \ **Category:** SketchUp SDK\ **Tags:** scaling, model\_units\ **Created:** [November 9, 2020, 5:40pm UTC](https://forums.sketchup.com/t/reading-drawing-scale-or-units/141783 "2020-11-09T17:40:43Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Richard8](https://avatars.discourse-cdn.com/v4/letter/r/e480ec/32.png) [@Richard8](https://forums.sketchup.com/u/Richard8)\ **Post date:** [November 9, 2020, 5:40pm UTC](https://forums.sketchup.com/t/reading-drawing-scale-or-units/141783/1 "2020-11-09T17:40:43Z")
(SketchUp C API) I have implemented a SketchUp “SKP” file importer for our 3D modelling package, and have discovered that the imported scale is _usually_ correct but is sometimes very wrong. SUModelGetUnits() returns SUModelUnits\_Meters for every model I have tested, and the vast majority of models are imported correctly if I accept this value and use a global scale factor of 1 skp unit == 1 metre. However, our users have discovered that a small number of SketchUp models are in fact 1 unit == 1 inch. I have not been able to determine any distinguishing features of these ‘inch’ models. In all these models, SUModelGetUnits() returns SUModelUnits\_Meters, and the “UnitsOptions” SUOptionsProvider returns 0 (Decimal) for LengthFormat and 4 (Metres) for LengthUnit. It doesn’t matter whether the model is really metres or really inches, I get the exact same results from these calls. How do I read the **actual** size of unit that is being used? ---
**Author:** ![DanRathbun](https://sea2.discourse-cdn.com/sketchup/user_avatar/forums.sketchup.com/danrathbun/32/500_2.png) [@DanRathbun](https://forums.sketchup.com/u/DanRathbun)\ **Post date:** [November 9, 2020, 6:43pm UTC](https://forums.sketchup.com/t/reading-drawing-scale-or-units/141783/2 "2020-11-09T18:43:07Z")
> [@Richard8](#): > > It doesn’t matter whether the model is really metres or really inches, I get the exact same results from these calls. The SketchUp application, and all it’s APIs internally uses inches for lengths and coordinates. ---
**Author:** ![Richard8](https://avatars.discourse-cdn.com/v4/letter/r/e480ec/32.png) [@Richard8](https://forums.sketchup.com/u/Richard8)\ **Post date:** [November 10, 2020, 10:29am UTC](https://forums.sketchup.com/t/reading-drawing-scale-or-units/141783/3 "2020-11-10T10:29:29Z")
Thanks. That is a very… shall we say “surprising” decision. It’s not very well documented in the SDK, I didn’t find that mentioned anywhere, though I assume it must be somewhere. I would certainly expect the actual units to be documented on the [SUPoint3D](https://extensions.sketchup.com/developers/sketchup_c_api/sketchup/struct_s_u_point3_d.html) page. ---
**Author:** ![DanRathbun](https://sea2.discourse-cdn.com/sketchup/user_avatar/forums.sketchup.com/danrathbun/32/500_2.png) [@DanRathbun](https://forums.sketchup.com/u/DanRathbun)\ **Post date:** [November 10, 2020, 5:16pm UTC](https://forums.sketchup.com/t/reading-drawing-scale-or-units/141783/4 "2020-11-10T17:16:11Z")
> [@Richard8](#): > > It’s not very well documented in the SDK, I didn’t find that mentioned anywhere, though I assume it must be somewhere. I agree. It **is** documented in the SketchUp **Ruby** API dictionary, in the **Overview** for the **[`Length`](https://ruby.sketchup.com/Length.html)** class. _viz:_ > _Internally, all lengths in SketchUp are stored in inches. The Length class stores values in inches as well. A number of methods have been added to the Ruby Numeric class to do units conversions._ The SketchUp Ruby API came many years before the C API, so it’s documentation is more robust. > [@Richard8](#): > > I would certainly expect the actual units to be documented on the [SUPoint3D](https://extensions.sketchup.com/developers/sketchup_c_api/sketchup/struct_s_u_point3_d.html) page. I agree that the description for the **coordinates** , **magnitudes** , **length** , **area** , and **volume** values, should explain that they are in inches (and that the internal tolerance is 0.001".) I opened an API Documentation Parity Issue for the C API in this regard. > > > \#### SketchUp C API Documentation Issue > > > ISSUE: The C API does not indicate …anywhere that SketchUp internal geometric values (and those stored in \*\*.skp\*\* and \*\*.layout\*\* file formats,) for \*\*length\*\*, \*\*area\*\* and \*\*volume\*\* are in \*\*inches\*\*. > > This causes problems for C API users unfamiliar with SketchUp and/or it's Ruby API. > > REF Public forum thread: \[Reading Drawing Scale (or Units)\](https://forums.sketchup.com/t/reading-drawing-scale-or-units/141783) > > \---- > > The description for the coordinates and magnitudes should have an additional ..."\`in inches.\`" for geometry structs: > \* \[\`SUPoint2D\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_point2\_d.html) > \* \[\`SUPoint3D\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_point3\_d.html) > \* \[\`SUVector2D\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_vector2\_d.html) > \* \[\`SUVector3D\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_vector3\_d.html) > \* \[\`SUUVQ\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_u\_v\_q.html) > > Certain submatrix values (ie, \*\*not\*\* the \*\*scale\*\* value) for: > \* \[\`SUTransformation\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_transformation.html) > \* \[\`SUTransformation2D\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_transformation2\_d.html) > > > Possibly the factors for the \[\`SUPlane3D\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_plane3\_d.html) equation. > > And in several places should explain SketchUp uses inches internally for \*\*length\*\*, \*\*area\*\*, and \*\*volume\*\* values, as well as storing such values in the SKP file format (and that the internal tolerance is 0.001".) > > Good places for this note (or link to it) might be: > > \* the \[Main\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/index.html) API introductory page (perhaps a \*\*Units\*\* section?) > \* \[\`SUEntitiesFill()\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_entities\_ref.html#a4c5230af9513a52f80ea9c7fdcf37a22) function > \* \[\`SUGeometryInputRef\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_geometry\_input\_ref.html) > \* \[\`SULengthFormatterRef\`\](https://extensions.sketchup.com/developers/sketchup\_c\_api/sketchup/struct\_s\_u\_length\_formatter\_ref.html) > > ~