Circuit for measuring high voltage DC voltage (up to 1000V)
A resistor divider will do what you want, but at this voltage there are some issues you can normally ignore: 

The top resistor has to be able to handle 1 kV.  Those are harder to get than "ordinary" resistors, and are often not linear with voltage at the high end.

Power dissipation.  Even what would normally be a "large" resistor, like 1 M&Omega;, dissipates a whole watt when 1 kV is applied to it.

You need physical distance between two points that have a kV between them for safety and to prevent arcing thru the air.



Due to all these reasons, I would implement the top resistor of the voltage divider with multiple more ordinary resistors in series.  For example, 0805 resistors are usually rated for 150 V (your job to check the datasheet).  Ten 1 M&Omega; 0805 resistor in series, physically laid out end to end, can be used as a 1 kV 10 M&Omega; resistor.  The voltage across each resistor will be 100 V or less, which keeps them within spec.

All together, the 10 M&Omega; string of resistors only dissipates 100 mW, so each individual resistor only 10 mW.  No problem here.

With a 10 M&Omega; top resistor, the bottom resistor of the divider would ideally be 25.06 k&Omega; to get 2.50 V out with 1000 V in.  You want to have a little headroom above the maximum input voltage spec of 1000 V, so a 24 k&Omega; or even a little lower bottom resistor should do it.

The output impedance of a divider with such a high ratio is basically the bottom resistor value.  24 k&Omega; may be too high for some A/Ds, so you may want to buffer this with a opamp used as voltage follower.