Question: I have a concrete floor and I made two holes to bolt a 1/4"-thick steel plate. The problem is that the steel plates haven't been drilled yet.

How can I determine where the holes will be drilled in the steel plates so they match the holes in the concrete?
[![enter image description here](https://i.stack.imgur.com/1Kt5n.png)](https://i.stack.imgur.com/1Kt5n.png)

Answer: 
I like Mark's answer best (create a paper template and mark the holes) but another technique came to mind.

Take a straightedge and a construction pencil.  

- Mark the centerline of the two holes longer than your steel plate.  

- Mark a line perpendicular, on each hole, wider than your plate.
- Put the plate down, use your straightedge and the marks to locate the hole centers.

[hmm. similar but different to Stanwoods solution which I did not see at first]
You need something with a slot in it, the same width as the bolts intended to go in the holes. Pass one bolt through, run a nut down and finger-tighten in place. Pass other bolt through, run a nut down it and tighten until you can slide the bolt easily along the slot. Now you have a gauge. Put your fixed bolt in one hole, slide the other along a slot until the bolt drops into the other hole. Tighten the nut with your fingers. Now the bolts are the correct distance apart.

Remove gauge from the concrete and use it indicate where to drill on the steel.