What size are bath taps, and will a new set fit my bath?
The three measurements that decide whether a bath tap fits — thread size, hole centres and rim thickness — and why bath taps are not basin taps.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 4 min
Short answer
UK bath taps are three-quarter inch BSP, basin taps are half inch, and they are not interchangeable. Standard bath tap hole centres are 180mm, so most two-hole baths take most bath taps. Check the hole centres, the hole diameter and the thickness of the rim the tap has to clamp through before you buy.
Almost every problem with buying bath taps comes from assuming that a tap is a tap. Bath taps are physically larger, use a larger thread, and are made to deliver a much higher flow rate than a basin tap, because a bath that takes twenty minutes to fill is a bath nobody uses. The good news is that the sizes involved are genuinely standardised, so a handful of measurements settle the question.
Step by step
- Note the thread size — three-quarter inch for a bath.UK bath taps have a 3/4 inch BSP tail; basin and kitchen taps are 1/2 inch. A bath tap will not screw onto a half-inch tap connector and vice versa without an adaptor, and adapting down to half inch throttles the fill rate, which defeats the point.
- Measure the hole centres.Centre of one tap hole to centre of the other, along the bath rim. The UK standard is 180mm, and almost every two-hole bath and every pair of pillar taps uses it. Some continental baths and some designer baths do not, so measure rather than assume.
- Measure the hole diameter.Typically around 28 to 30mm on a bath. A tap with a larger tail will not go through a smaller hole, and enlarging a hole in acrylic is possible with a hole saw but enlarging one in enamel is not sensible.
- Measure the rim thickness the tap has to clamp.This is the one that catches people out. The tap's tail has a limited threaded length, and it has to pass through the bath rim, take a washer and a backnut, and still have thread left. A thick reinforced acrylic rim or a stone resin bath can be too thick for a short-tailed designer tap — check the tap's stated maximum rim thickness.
- Check the number of holes you have.Two holes take a pair of pillar taps or a two-hole bath filler. One hole takes a monobloc bath filler. Three holes take a bath mixer with a separate spout and two handles. Four or five holes are a deck-mounted set with a shower handset. You cannot fill a redundant hole in a bath invisibly, so the new tap needs to use the holes you have.
- Check whether you need low-pressure taps.Taps are rated for a minimum working pressure. A gravity-fed tank system upstairs can deliver very little head to a first-floor bath, and a tap designed for mains pressure will trickle. If your hot water comes from a cylinder in an airing cupboard with a tank in the loft, buy taps rated for low pressure.
- Decide about flexible tails and isolating valves at the same time.Buying taps with flexible tails, or fitting flexible tap connectors, turns a future tap change from a contortion into a twenty-minute job. Fit isolating valves in the tails while the panel is off.
Tips
- Take a photograph of the underside of the existing taps before you order. The connection arrangement tells you more than any measurement.
- A bath shower mixer needs a diverter and a hose outlet, and its shower performance is limited by the water system feeding it, not by the tap. On a gravity system without a pump, expect a modest spray.
- Wall-mounted bath taps solve the rim thickness question entirely, but they need pipework in the wall behind and are not a swap for deck taps.
Questions people ask
Are bath tap holes always 180mm apart?
In the UK, almost always. It is the de facto standard for two-hole baths and pillar tap sets. Measure anyway, because imported and designer baths do vary and a 20mm error means the taps will not go on.
Can I use basin taps on a bath?
Physically you can adapt them, but you should not. They are half-inch, so the fill rate drops to the point where the bath takes an unreasonable time, and the spout usually will not reach far enough over the rim.
What does 'low pressure' mean on a tap?
It means the tap is designed to give a usable flow at low head — typically stated as a minimum bar figure. Gravity-fed systems from a loft tank produce roughly 0.1 bar per metre of height between tank and tap, which is very little on a first floor.