Kilogram-force per Square Centimeter to Foot Water (4 °C)

One technical atmosphere (symbol "at") is defined as exactly 1 kgf/cm² — the pressure exerted by a 1 kg mass on a 1 cm² area under standard gravity. It equals 98,066.5 Pa, roughly 3.6% less than a standard atmosphere (101,325 Pa). Russian and Japanese engineering standards used it heavily through the 20th century, and you will still find it on older boiler plates, hydraulic presses, and pressure vessel nameplates across Asia and Eastern Europe.

Japanese Industrial Standards (JIS) and Soviet-era GOST standards specified kgf/cm² for decades, and millions of gauges, compressors, and hydraulic machines built to those specs remain in service. Replacing a working gauge just to change the scale is wasteful, so factories keep using kgf/cm² alongside newer SI instruments. Modern JIS standards accept both, but legacy equipment is everywhere.

Multiply kgf/cm² by 14.22 to get psi, or by 0.981 to get bar. For quick mental math: 1 kgf/cm² ≈ 1 bar ≈ 14.2 psi ≈ 1 atmosphere. The errors in those approximations are all under 4%, which is close enough for field work. For precision, use the exact factor: 1 kgf/cm² = 98,066.5 Pa.

Small hydraulic jacks operate at 50–100 kgf/cm². Excavator hydraulics run at 250–350 kgf/cm². Industrial presses for stamping car body panels can reach 500–1,000 kgf/cm². The highest-pressure hydraulic systems — used in forging and isostatic pressing — operate above 3,000 kgf/cm², squeezing metal powder into near-net-shape parts.

Officially, yes — the SI discourages kilogram-force entirely, and international standards bodies prefer pascals, bar, or psi. Practically, the phase-out is glacially slow. New equipment in Japan and Russia increasingly uses MPa or bar, but service manuals, legacy calibrations, and replacement parts will reference kgf/cm² for decades to come. Knowing the conversion (×0.0981 for MPa) remains a useful skill for anyone working with imported machinery.

Because every foot of elevation equals exactly 1 ftH₂O of pressure at the tap below. A comfortable shower needs about 20–25 ftH₂O, and a fire hydrant demands 40–60 ftH₂O. So a water tower serving a flat town typically stands 40–60 feet above rooftop level to guarantee adequate pressure during peak demand. Taller buildings in the service area need even more height — or booster pumps — because each story above ground "uses up" about 10 ftH₂O of the tower's gravity-supplied head.

1 ftH₂O = 0.4335 psi. So divide psi by 0.4335 (or multiply by 2.31) to get feet of head. A city water main at 60 psi delivers about 138 ft of head — enough to reach the 12th floor of a building by gravity alone. This 2.31 factor is worth memorising if you work in US plumbing or fire-protection engineering; it pops up in every pipe-sizing calculation.

Because the physical setup is literally vertical — a well pump sits at the bottom of a hole and pushes water up. Saying "the pump needs 150 feet of head" maps directly to the well depth plus the elevation to the pressure tank. Converting to psi (65 psi) loses that physical clarity. Fire-sprinkler designers think the same way: "how high does water need to climb?" is answered in feet, not pounds.

1 ftH₂O = 12 inH₂O, just as 1 foot = 12 inches. Inches of water are used for low-pressure air systems (HVAC ducts at 0.1–4 inH₂O), while feet of water handle higher liquid pressures (municipal water at 40–140 ftH₂O). The two scales cover different engineering domains but share the same underlying physics — pressure from a column of water at 4 °C under standard gravity.

About 1 atmosphere (14.7 psi). Divers learn the "33 feet" rule: every 33 feet of seawater adds 1 atm of pressure. (Fresh water is slightly less dense, so the equivalent is about 34 feet.) At 100 feet, a diver is under roughly 4 atm total — 3 gauge plus 1 atmospheric. This is why recreational dive limits are set at 130 ft (about 5 atm) — beyond that, nitrogen narcosis becomes a serious risk.