Measure centre to centre, not edge to edge, and expect 150 mm. That figure is the continental European convention for wall-mounted bath and shower mixers, and a tap built for it will not sit on a pair of outlets at 140 or 160 mm without help.
How to measure it
Put a tape across the two wall outlets and read the distance between their centres. Measuring between the inside edges gives you a smaller number and buys the wrong tap.
When the number is not 150
Older installations, and walls that moved during a renovation, produce anything from about 140 to 170 mm. The fix is eccentric connectors — S-shaped unions that screw into the wall outlets and let the tap be adjusted sideways by a centimetre or two each side. Most bar mixers are sold with them; when they are not, they cost a few euros.
The other measurement
Spout reach, which decides whether water lands in the bath or runs down the inside wall. A short spout on a wide bath rim is the second most common regret in this family.
Questions people actually ask
How much adjustment do eccentric connectors give?
Typically about 10 to 20 mm each side, so roughly 130 to 170 mm from a 150 mm tap. The manufacturer states the range; beyond it, the wall outlets have to move.
Does a deck-mounted bath filler use the same measurement?
No. A deck-mounted filler is set by the hole spacing drilled in the bath rim, and by whether the rim is thick enough for the fixing. It is a different measurement entirely.
Last reviewed 5 September 2026