2.5" HDD power consumption

No there isn't, but you shouldn't rely on that measurement you made anyway. The heaviest current draw occurs while the drive is spinning up. Look at the datasheet for the specific drive you're using to see what that might be.

If you are using whatever random drive happens to be available off the shelf, budget for a momentary current drain of 1A. This is the assumption made by USB hard drive enclosures (the type with a "Y" cable so they can pull current from two ports at once) and it is practically always sufficient.

OK, thanks. I haven't actually done any measurements yet, the figures I quoted were the ones printed on the drive labels.

What's printed on the labels will be the condensed version of the specs. It's a funny thing, but the manufacturers almost always leave the really awkward stuff in the data sheet and not on the label.

You should be able to find the data sheets on the manufacturer's web site or by some careful web searching.

If power is a concern have you considered 1.8" or smaller hard disk drives?

Figure 4 contains rather useful information regarding the current draw of various HD sizes:

Interesting, thanks. The 2.5A max figure for 2.5" drives looks a bit high - I've pulled the specs for a few current-generation HDDs off the web, along with those for the 4-5yr old ones we have lying around, and I can't find any that draw more than 1 A during spin-up. We chose 2.5" for development as there is a ready supply of these scrounged from dead laptops and it makes for a tidier desk, no issues with power sequencing, etc. This is for lab use only, the product never gets shipped with a HDD.

Looks like their figures are on the conservative side, to make sure that most of the worst case drives are covered.

In that case hanging a huge electrolytic onto that power node might help tide it over the spool-up spike. But be careful especially when you use LDO regulators since they can then go berserk.