I know this one is easy - but I can't figure it out.

I am doing a room drawing in visio. I am using walls doors and window shapes. I have the four walls and a door done. My issue is - one wall I have drawn says it is 61 feet. In reality it is 10 feet. If I edit the shape data and set it to 10 feet - the object in the drawing gets smaller.

There must be a ratio somewhere that says 1" = xxxxx. But where us that?