The Unit Everyone Understands, Made Exact
Meteorology reports 1013 hPa on a weather map. Engineering drawings quote 250 kPa. Dive computers count in atmospheres. All three are the same physical scale, and the atmosphere is the one with the intuitive hook: it is the pressure you have lived under your whole life. When a pressure vessel is rated "3 atm", a technician knows instantly it holds three times sea-level pressure; when it is rated 303.98 kPa, they reach for a calculator. This converter is that calculator — divide by 101.325, the exact definition of the standard atmosphere, and SI numbers come back as something the whole team can feel.
atm = kPa ÷ 101.325
1 atm = 101,325 Pa exactly
Definitional — divide by the standard atmosphere and the number becomes intuitive.
SI Pressures, Translated to Atmospheres
| kPa | atm | Context |
|---|---|---|
| 50.66 kPa | 0.5 atm | Cabin pressure at 8,000 ft cruise altitude. |
| 101.3 kPa | 1 atm | Sea level — the weather map's 1013 hPa. |
| 202.65 kPa | 2 atm | Diver at 10 m (absolute). |
| 250 kPa | 2.47 atm | Passenger tire — about 2.5 atmospheres. |
| 303.98 kPa | 3 atm | Autoclave sterilization cycle. |
The tire row carries a subtlety worth stating plainly: a 250 kPa tire is 2.47 atm of gauge pressure — the pressure above the atmosphere — while the absolute pressure inside is about 3.5 atm. Dive tables and pressure-vessel codes use absolute; tire gauges and shop compressors read gauge. The gap between them is exactly 1 atm (101.325 kPa), and forgetting it is one of the classic unit errors in the pressure world — the same reason this page's FAQ warns against reading "1 atm" as "100 kPa" (that 1.3% slip is the difference between the atmosphere and the bar).
Engineering Context
The forward direction is atm to kPa. This pair completes the atmosphere row of the pressure hub: Pa to atm and atm to Pa for the raw pascal, psi to atm and atm to psi for the American gauge, and bar to kPa / kPa to bar for the bar, the atmosphere's round-number cousin. Diving, weather, and pressure-vessel work all route through the pressure hub.
More: atm to kPa · Pa to atm · kPa to bar · Pressure Hub
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Frequently Asked Questions
How do I convert kPa to atm?
Divide by 101.325: atm = kPa ÷ 101.325. A 250 kPa tire is 250 ÷ 101.325 = 2.47 atm. The standard atmosphere is defined as 101.325 kPa, so the factor is exact.
How many atmospheres is a car tire?
About 2.5: a 250 kPa tire is 2.47 atm, and a US-spec 36 psi tire is 2.48 atm. Note that a tire gauge reads gauge pressure — the pressure above the atmosphere — so the absolute pressure inside is about 3.5 atm. Tire inflation is one of the few places engineers mix gauge and absolute without saying so.
Does 1 atm equal 100 kPa?
No — 1 atm is 101.325 kPa; 100 kPa is exactly 1 bar. The two round-looking numbers are a classic source of error: an atmosphere is 1.3% larger than a bar. A design spec written as '1 atm' and interpreted as '100 kPa' is short by 1.325 kPa, which at 300 atm of vessel pressure becomes a 4 bar gap.
More: atm to kpa · pa to atm · Pressure Hub