No more than 2 or 3 mm.
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Oh, well done David... those antennae did look interesting, but I couldn't work out their structure.
Obviously I spent too long writing as well... :o)
I'm afraid there's probably not enough information in the photo to get very far. It doesn't look like a bug to me (although it's possible that it could be a small pentatomoid - I'm not sure what other species there are in Sweden), but much more likely it's a beetle. There are thousands of small dark beetle species, and I wouldn't even like to pick a family here...
Any chance you could get a much better image? If you don't have access to a camera that can do macrophotographs, a detailed drawing can be useful, at least to get a rough idea what it is.
Attagenus smirovi is a well known synanthropic species and the most likely beetle with this shape of antenna to be regularly found in houses in the UK, probably the same in Sweden. It's also well known as a museum pest.
Not one I ever found when doing the pest trapping in Leeds, or in any houses I've lived in. I'm always struck how synanthropic things that are common and widespread are also sometimes very patchy... we had a fine collection of rare (and even new to UK) booklice in our stores instead...
If I see it again i'll try for a better image... Some people have said Bed Bug, Cimex lectularius.
Definitely not a bed bug - it's a very distinctive beastie, so don't worry. I'm pretty sure the id above is correct, but a better picture will certainly help.
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