TradeCalculator.co.uk
Water Pressure Calculator — Is My Pressure Sufficient?
Calculate water pressure from head height or mains supply, including pipe friction losses. Check if your pressure is adequate for showers and taps.
Typical UK: 1.0-4.0 bar. Check with a gauge.
Total pipe length from source to fixture
Each elbow adds ~0.6m equivalent length
Equivalent pipe length per elbow/bend (default 0.6m)
Shower pump pressure boost for pumped systems (default 1.5 bar)
Next up: related pages
How We Calculate This
This calculator estimates the effective water pressure at a fixture by starting with the available pressure (from gravity head or mains supply) and subtracting friction losses through the pipe run.
The formulas
Gravity pressure (bar) = Head height (m) × 0.0981 (1 m of water head = 0.0981 bar; ≈0.1 bar is the common site rule of thumb)
Equivalent pipe length = Actual length + (Elbows × 0.6m)
Friction loss uses the Hazen-Williams equation: hf = 10.67 × L × Q1.852 ÷ (C1.852 × d4.87), with flow Q in m³/s, internal diameter d in m, length L in m and roughness C = 130 for new copper. The head loss in metres is converted to bar at 0.0981 bar/m.
Effective pressure = Available pressure − Friction loss
Internal bores follow BS EN 1057 copper tube: 15 mm OD = 13.6 mm bore, 22 mm = 20.0 mm, 28 mm = 26.2 mm, 35 mm = 32.6 mm, 42 mm = 39.6 mm, 54 mm = 51.6 mm. Because friction scales with d4.87, stepping up one pipe size roughly halves to quarters the loss.
Fixture minimum pressures
- Basin/bath tap: 0.1 bar
- Kitchen tap: 0.5 bar
- Mixer shower: 0.1 bar
- Thermostatic shower: 0.5 bar
- Power shower: 1.0 bar
- Electric shower: 1.0 bar
- Rain head shower: 1.5 bar
Note: This is a simplified calculation. Real-world pressure depends on many factors including pipe condition, simultaneous demand, and water company supply pressure. For accurate results, use a pressure gauge at the fixture location.
Frequently Asked Questions
UK mains water pressure typically ranges from 1.0 to 4.0 bar, with most properties receiving 2-3 bar. Under Ofwat's Guaranteed Standards Scheme, water companies must maintain a statutory minimum of 0.7 bar (7 metres of static head) in the communication pipe at the property boundary — most companies aim higher, around 1.0 bar (10 m head), as a service target. Pressure varies by location, time of day, and demand in the area. You can check yours with a pressure gauge on an outside tap.
For gravity-fed systems (cold water tank in the loft), pressure depends on the vertical height between the tank and the outlet. Every 1 metre of height (head) provides 0.1 bar of pressure. So a tank 3 metres above the shower gives 0.3 bar — which is low and often insufficient for thermostatic showers or rain heads.
Most thermostatic shower valves require a minimum of 0.5 bar (some need 1.0 bar). Gravity-fed systems often can't provide this without a pump. Combi boilers and unvented cylinders typically provide 1.5–3.0 bar, which is adequate. Always check the manufacturer's minimum pressure requirement. See our TMV Sizing Calculator for thermostatic mixing valve flow rates.
On mains-fed systems, water pressure decreases by approximately 0.1 bar for every metre of height. A bathroom 6m above the mains entry point loses about 0.6 bar. Additionally, pipe friction from longer runs and more bends further reduces pressure. This is why first-floor bathrooms sometimes have lower shower pressure than ground-floor ones.
Options include: (1) Install a shower pump (for gravity systems), (2) Switch to a combi boiler or unvented cylinder for mains pressure throughout, (3) Reduce pipe friction by using larger diameter pipes or shorter runs, (4) Install a mains booster pump (check with your water company first), (5) Ensure the stopcock is fully open and pipes are not furred up. A Water Softener Calculator can help if limescale build-up is restricting flow, and our Water Loading Units Calculator can confirm your supply is adequate for the number of outlets.
Was this calculator helpful?
Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.