mmH2O to inH2O Converter
Pressure · unit-converter
Convert mmH2O to inH2O with a fixed input and output unit, step-by-step formula line, and reference tables. All calculations bridge through pascal with fixed definitions (standard atmosphere = 101,325 Pa; torr and mmHg = atm/760; plus industrial/manometer units like kgf/cm², inHg, inH2O, and mmH2O).
About mmH2O
Millimeters of water column (mmH2O) is used for very low differential pressure in instrumentation and ventilation.
About inH2O
Inches of water column (inH2O) is common in low-pressure HVAC and duct static-pressure measurements.
How to convert millimeter of water (mmh2o, 4 °c) to inch of water (inh2o, 4 °c)
1 mmh2o equals 0.03937007874015748 inh2o in this tool (via pascal):
1 mmh2o = (9.80665 Pa ÷ 249.08891 Pa) inh2o = 0.03937007874015748 inh2o
Each mmh2o carries 9.80665 Pa and each inh2o 249.08891 Pa, so one mmh2o equals 9.80665 ÷ 249.08891 inh2o.
Let p(mmh2o) be pressure in mmH2O (mmh2o), and p(inh2o) in inH2O (inh2o). Then:
p(inh2o) = p(mmh2o) × (9.80665 / 249.08891)
Equivalently, divide by how many mmh2o fit into one inh2o (Pa per inh2o divided by Pa per mmh2o):
p(inh2o) = p(mmh2o) ÷ 25.400000000000002
Examples
Example #1: Convert 1 mmh2o to inh2o
1 mmh2o = 1 mmh2o × (9.80665/249.08891) inh2o = 0.0393700787 inh2o
1 mmh2o = 1 mmh2o ÷ 25.400000000000002 = 0.0393700787 inh2o
1 mmh2o × (9.80665/249.08891) = 0.039370 inh2o
Example #2: Convert 10 mmh2o to inh2o
10 mmh2o = 10 mmh2o × (9.80665/249.08891) inh2o = 0.3937007874 inh2o
10 mmh2o = 10 mmh2o ÷ 25.400000000000002 = 0.3937007874 inh2o
10 mmh2o × (9.80665/249.08891) = 0.393701 inh2o
Summary
To convert mmH2O to inH2O, multiply the value in mmh2o by (9.80665 Pa per mmh2o) / (249.08891 Pa per inh2o). Equivalently: value_inh2o = value_mmh2o × (9.80665 / 249.08891). Numerically, 1 mmh2o equals 0.03937007874015748 inh2o.
Relationship context
Both mmH2O and inH2O are converted by fixed multiples of the pascal. Multiplying by (Pa per mmh2o) ÷ (Pa per inh2o) gives the same result as passing through pascal, keeping bar, atm, PSI, kPa, hPa, torr, and mmHg consistent on the hub.
Conversion tables
| mmH2O (mmh2o) | inH2O (inh2o) |
|---|---|
| 0.1 | 0.0039370079 |
| 1 | 0.0393700787 |
| 2 | 0.0787401575 |
| 3 | 0.1181102362 |
| 4 | 0.157480315 |
| 5 | 0.1968503937 |
| 6 | 0.2362204724 |
| 7 | 0.2755905512 |
| 8 | 0.3149606299 |
| 9 | 0.3543307087 |
| mmH2O (mmh2o) | inH2O (inh2o) |
|---|---|
| 10 | 0.3937007874 |
| 20 | 0.7874015748 |
| 30 | 1.1811023622 |
| 40 | 1.5748031496 |
| 50 | 1.968503937 |
| 60 | 2.3622047244 |
| 70 | 2.7559055118 |
| 80 | 3.1496062992 |
| 90 | 3.5433070866 |
| 100 | 3.937007874 |