Activate the Line tool.
Start drawing a line.
Click the start point.
Drag the cursor towards the end point.
The measurement box will show the changing length of it.
When it is near the desired size you can click the end point.
Now immediately type in the exact length required.
For example:
16'3"
The press enter.
Using the unit suffixes.
The line should now be exactly that length.
Do not click on the measurements-box - just type the size + enter, immediately after drawing the line and before doing anything else - this approach applies to most creating geometry like circle-radius etc too…
To check it Select the line and look at ‘Entity Info’.
If its length is not being reported in the units you want perhaps the model has the wrong Units set up in Model Info…
Change those to suit what you want - although you can type in using any units with a suffix, If the model-units are set as inches then typing in 16 is taken as 16", but 16' in feet, 16cm is in centimeters etc.
There are many ways to draw exact geometry - snapping, typing, using guides etc - check the video tutorials.