handlebar stem measurement

[alecstilleyedye]

i'm considering changing the stem on my roadbike from the one it came with from new. i want one that is 90° (ie flat), not sloping. i need to know what length the current one is, where does one measure where to where to find the right length?

[Sergeant Pluck]

Centre to centre: centre of the bars to centre of the stem. If you take the old stem off, some brands have it stamped inside the stem clamp.

[eck]

By "flat" do you mean horizontal / at 90 degrees to the ground? AFAIK, a 90 degree stem means it's at 90 degrees to the steerer tube, so it will point up.  Perhaps what you want is a "zero degree rise"? 

EDIT: my mistake - as usual - yes parallel to the ground. Thank you Mr MSeries.

[MSeries]

I would say he means horizontal/zero or 180 degrees to the ground.

The labelling differs for different brands. I have seen some labelled 17 deg, which gives them horizontal on a 73 degree headtubed bike.

But some are more sensibly labelled wrt to the head tube angle

E.g. Cinelli VAI, is 73/107 for the longer ones, 84/96 for the shorter.

whereas the Raceface prodigy is 8 deg