Know exactly how much pressure your tank delivers — and how high it needs to be. Six free tools covering water pressure, pump head, gravity-feed flow, hydrostatic loads, and the minimum elevation required for a working shower.
In a gravity system, water pressure is determined almost entirely by height — every foot of water gives 0.433 psi, and every metre about 0.1 bar. Whether your system relies on gravity or a pump, understanding the relationship between elevation and pressure is what separates a system that works from one that frustrates you daily. This category contains six calculators targeting every stage of that problem: finding out how much pressure your current tank delivers, sizing a pump to hit a target pressure, checking that gravity-feed flow is sufficient for your application, verifying that your tank structure can withstand hydrostatic loads, converting between pressure units for different trades, and calculating the exact minimum tank elevation needed for a functional shower.
These tools are used by homeowners sizing rooftop water storage, plumbers specifying pipe and pump combinations, civil engineers designing gravity irrigation systems, and anyone setting up an off-grid water supply. Each calculator gives instant results in US and metric units (psi and feet first, with bar, kPa and metres alongside), shows its working, a worked example and its sources, and has been reviewed by John Mac, PE. No sign-up is required.
🧭 How to Choose
How to Choose the Right Calculator
Start with: what problem are you solving?
If your system is gravity-fed and you want to know the pressure at a tap or outlet, use the Water Pressure Calculator. Feed it your tank height and you get instant bar/PSI/kPa results. This is the most commonly needed tool in this category.
You're buying or sizing a pump
Gravity alone isn't enough for many residential or agricultural setups. The Pump Head Pressure Calculator accounts for static lift plus pipe friction to give you the total dynamic head — the number on every pump datasheet. Use this before spending money on a pump.
You need to know if gravity-feed flow rate is sufficient
Pressure alone doesn't tell you whether enough water will flow. The Gravity Feed Flow Rate Calculator models head height, pipe diameter, and pipe length together to give you a flow rate estimate. If the result is too low, a larger pipe is usually the most effective fix; raising the tank helps less than you might expect, and a pump is the last resort.
You're specifying or verifying a tank's structural integrity
The Hydrostatic Pressure Calculator tells you the pressure acting on any point in a tank's wall or base. Use it as the starting point when checking that a tank, fitting or valve you're buying is rated for the job — and always get large, tall or buried tanks checked by the manufacturer or an engineer.
You need to convert pressure units or verify a shower installation
The Water Column Pressure Calculator handles unit conversions between all common pressure formats. For shower installations specifically, the Minimum Tank Height for Shower Pressure Calculator takes the pressure your shower needs, the pipe friction and a safety margin, and returns the minimum tank height above the shower head and above ground.
Your Situation
Use This Calculator
Key Output
Gravity tank, check outlet pressure
Water Pressure Calculator
bar / PSI / kPa
Buying a pump, need head spec
Pump Head Pressure Calculator
Total dynamic head (m)
Check if gravity flow rate is enough
Gravity Feed Flow Rate Calculator
L/min or GPM
Design or verify tank wall rating
Hydrostatic Pressure Calculator
Pressure at depth (bar)
Convert pressure units
Water Column Pressure Calculator
m WC / in WC / bar / kPa / PSI
Gravity shower, check height needed
Min Tank Height for Shower Pressure
Minimum height (m / ft)
✅ Sources & Review
How These Calculators Are Built and Reviewed
The calculators in this category rest on two standard pieces of physics — hydrostatic pressure (P = ρgh, or 0.433 psi per foot of water) and pipe friction (the Hazen-Williams equation) — and each one shows its working so you can check the numbers. The constants and practical figures come from these references:
University of Kentucky Cooperative Extension — HO-120: drip irrigation pressures and tank heights.
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.
Last updated
❓ FAQ
Frequently Asked Questions
How do I calculate water pressure from a rooftop tank?
Water pressure from a gravity-fed rooftop tank is determined by the vertical height (head) of water above the outlet. The formula is: Pressure (bar) = Height (m) × 0.0981, or in PSI: Pressure (psi) = Height (ft) × 0.433. A tank positioned 10 metres above a tap delivers approximately 0.98 bar (14.2 psi) of static pressure. Use the Water Pressure Calculator to run this instantly.
What is the minimum tank height needed for a good shower?
Showers and valves made for low-pressure gravity systems are commonly rated to work from about 0.1 bar (1.5 psi) — roughly 1 metre (3.3 ft) between the bottom of the tank and the showerhead — though the flow is gentle there. Around 0.5 bar (7 psi, 5 m / 17 ft) gives a comfortable gravity shower; many standard valves and heads list 1 bar (14.5 psi, 10 m / 33 ft) or more. In the US, plumbing codes size the supply for at least 8 psi flowing at a shower. A pumped "power shower" or a booster pump is the usual answer when the tank cannot go higher. Our Minimum Tank Height for Shower Pressure Calculator handles this for any showerhead type.
What is the difference between static and dynamic water pressure?
Static pressure is the pressure in a system when water is not flowing — determined purely by the height of the water column. Dynamic (residual) pressure is the pressure at a tap while water is actually flowing. Dynamic pressure is always lower than static because pipe friction consumes available head. The water pressure, hydrostatic and water column calculators give static pressure; the shower height calculator lets you add pipe friction, and the Gravity Feed Flow Rate Calculator works out the friction from pipe size, length and flow.
How do I convert metres of water head to bar or PSI?
In US units, 1 foot of water head = 0.433 psi, and 1 psi = 2.31 ft. In metric, 1 metre of water head = 0.0981 bar = 1.422 psi = 9.81 kPa, so 10 metres of head produces 0.981 bar or roughly 14.2 psi. In reverse: 1 bar = 10.2 metres of head. The Water Column Pressure Calculator handles all these conversions in both directions automatically.
The pump must overcome total dynamic head: vertical lift (static head) + pipe friction losses + any required delivery pressure. Friction depends heavily on the flow and pipe size, so a fixed percentage can be far off. For example, lifting water 10 m (33 ft) through 20 m (66 ft) of 25 mm (1") plastic pipe adds only about 0.5 m of friction at 20 L/min (5 GPM), but about 1.7 m at 40 L/min (10.6 GPM) — and much more in narrower pipe. The Pump Head Pressure Calculator handles this precisely based on actual pipe parameters.
What is hydrostatic pressure and why does it matter for tank design?
Hydrostatic pressure is the pressure exerted by a fluid at rest due to the weight of water above a given point. At the base of a full tank holding water 6.5 ft (2 m) deep, the hydrostatic pressure is approximately 2.84 psi (0.196 bar). This matters because tank walls and base fittings must be rated to handle this pressure — which increases linearly with depth, so the bottom of a tall tank carries the most. Underrated tanks can bulge, crack or leak at connection points. Use the Hydrostatic Pressure Calculator to determine pressure at any depth before specifying materials.
