Pound per Square Inch to Meter Water (4 °C)
psi
mH2O
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 psi (Pound per Square Inch) → 0.70308927 mH2O (Meter Water (4 °C)) Just now · Rounding: Up to 8 significant figures | Recalculate this conversion using your current rounding settings. |
Quick Reference Table (Pound per Square Inch to Meter Water (4 °C))
| Pound per Square Inch (psi) | Meter Water (4 °C) (mH2O) |
|---|---|
| 0.1 | 0.070308927 |
| 1 | 0.70308927 |
| 14.696 | 10.3326 |
| 30 | 21.092678 |
| 60 | 42.185356 |
| 100 | 70.308927 |
| 3,000 | 2,109.2678 |
Results rounded to a maximum of 8 significant figures
About Pound per Square Inch (psi)
The pound per square inch (psi) is the dominant pressure unit in US customary practice, equal to approximately 6,894.76 pascals. It is universally used in the United States for tire pressures, compressed-air systems, hydraulic machinery, pipe pressure ratings, and industrial gauges. Standard atmospheric pressure is 14.696 psi. Pressure is expressed as gauge (psig, relative to atmosphere) or absolute (psia). Natural gas pipeline pressures, boiler ratings, and municipal water supply pressures in the US are all quoted in psi.
Car tire inflation is typically 30–35 psi. A standard garden hose delivers water at 40–60 psi.
Etymology: A straightforward compound of "pound" (from Latin pondus, weight) and "square inch", arising naturally from US customary engineering practice. There is no single defining event; the unit crystallised alongside the development of American steam engineering in the early 19th century.
About Meter Water (4 °C) (mH2O)
The meter of water at 4 °C (mH₂O) equals 9,806.3754138 pascals under the fixed-density reference and standard gravity. It is used in hydrology, hydraulics, and pump engineering to express gauge pressures in water systems. Pump head and pipeline friction losses in water distribution are quoted in meters of water column. Every 10 meters of seawater depth adds approximately 1 bar of pressure, making this unit intuitive for diving and underwater engineering.
A 10 m swimming pool depth corresponds to 10 mH₂O of gauge pressure. Municipal water mains typically operate at 20–60 mH₂O.
Pound per Square Inch – Frequently Asked Questions
Why do race car teams obsess over half-psi differences in tire pressure?
Because at racing speeds, tiny pressure changes transform tire behavior. Half a psi less inflates the contact patch, generating more grip but also more heat — potentially pushing the rubber past its optimal temperature window within a few laps. Half a psi more stiffens the sidewall, improving response but shrinking the contact patch and reducing peak grip. Formula 1 teams adjust pressures in quarter-psi increments based on track temperature, fuel load, and stint length. In NASCAR, a 1 psi difference between left and right tires is a deliberate setup tool that changes how the car rotates through banked turns.
What psi should car and bicycle tires be inflated to?
Passenger car tires: 30–35 psi (check the door jamb sticker, not the tire sidewall — the sidewall shows the maximum, not the recommended). Truck tires: 80–100 psi. Road bike tires: 80–130 psi. Mountain bike tires: 25–35 psi. Under-inflation by just 5 psi increases fuel consumption by about 2% and accelerates edge wear. Over-inflation reduces grip and makes the ride harsh.
What is the difference between psi, psig, and psia?
PSI is the generic unit. PSIG ("gauge") means pressure above atmospheric — what your tire gauge reads. PSIA ("absolute") includes atmospheric pressure on top: PSIA = PSIG + 14.7. A tire at 32 psig is actually at 46.7 psia. The distinction matters in engineering calculations involving gas laws (PV=nRT uses absolute pressure) and in vacuum work where gauge readings go negative.
What psi range do common household and industrial systems use?
City water supply: 40–80 psi. Home espresso machine: ~130 psi (9 bar). Pressure washer: 1,000–4,000 psi. Scuba tank: 3,000 psi. Hydraulic car jack: 3,000–10,000 psi. Diesel fuel injector rail: up to 30,000 psi. Waterjet cutter: 60,000+ psi. The range from a garden hose to an industrial waterjet spans roughly three orders of magnitude.
How do you quickly convert between psi and bar in your head?
Divide psi by 14.5 to get bar, or multiply bar by 14.5 to get psi. For even quicker estimates: 15 psi ≈ 1 bar, 30 psi ≈ 2 bar, 45 psi ≈ 3 bar. This "15 psi per bar" shortcut is within 2% of exact and is used by mechanics, divers, and engineers worldwide when a calculator is not handy.
Meter Water (4 °C) – Frequently Asked Questions
Why do pump specifications use "meters of head" instead of bar or psi?
Because pump engineers think in terms of how high the pump can lift water. A pump rated at 30 mH₂O can push water 30 meters straight up — no conversion needed to figure out if it can reach the tenth floor. The unit also makes friction-loss calculations intuitive: if a 100-meter horizontal pipe run has 5 mH₂O of friction loss, you subtract that directly from the pump's head rating.
How deep underwater do you need to go to reach 1 mH₂O of gauge pressure?
Approximately 1 meter in fresh water. The unit references water at 4 °C under standard gravity; actual column pressure depends on water density and local gravity, so a real pool does not necessarily reproduce that reference exactly. Seawater is about 2.5% denser, so 1 meter of seawater corresponds to roughly 1.025 mH₂O of gauge pressure.
What is the typical water pressure in a house in mH₂O?
Municipal water mains deliver 20–60 mH₂O (roughly 2–6 bar or 30–85 psi) at the meter. A gravity-fed rooftop tank 10 meters above the tap provides about 10 mH₂O — barely enough for a decent shower, which is why booster pumps are common in buildings with rooftop storage. High-rise buildings need pressurisation systems because gravity alone cannot push water above about 60 mH₂O without boosting.
How does mH₂O relate to bar and atmospheres?
10.33 mH₂O ≈ 1 atmosphere ≈ 1.013 bar. For quick math: 10 mH₂O ≈ 1 bar (error about 2%). This rule of thumb is used constantly in plumbing and fire protection: a building with a water tank 40 m above ground level has roughly 4 bar of static pressure at the base. Multiply meters by 0.1 and you have bar — close enough for pipe sizing.
Why is the "4 °C" reference important for water column pressure units?
Temperature affects water density and therefore column pressure. The 4 °C reference is close to water's maximum density and specifies the conditions for comparing water-column units. This converter uses the fixed reference density of 999.972 kg/m³ and standard gravity, producing 9,806.3754138 Pa per meter. The metric and imperial factors retain the complete result while preserving their exact height relationships. This computational precision does not imply that a real manometer reproduces the reference density or gravity exactly.