inH2O to mmH2O Converter
Pressure · unit-converter
Convert inH2O to mmH2O 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 inH2O
Inches of water column (inH2O) is common in low-pressure HVAC and duct static-pressure measurements.
About mmH2O
Millimeters of water column (mmH2O) is used for very low differential pressure in instrumentation and ventilation.
How to convert inch of water (inh2o, 4 °c) to millimeter of water (mmh2o, 4 °c)
1 inh2o equals 25.400000000000002 mmh2o in this tool (via pascal):
1 inh2o = (249.08891 Pa ÷ 9.80665 Pa) mmh2o = 25.400000000000002 mmh2o
Each inh2o carries 249.08891 Pa and each mmh2o 9.80665 Pa, so one inh2o equals 249.08891 ÷ 9.80665 mmh2o.
Let p(inh2o) be pressure in inH2O (inh2o), and p(mmh2o) in mmH2O (mmh2o). Then:
p(mmh2o) = p(inh2o) × (249.08891 / 9.80665)
Equivalently, divide by how many inh2o fit into one mmh2o (Pa per mmh2o divided by Pa per inh2o):
p(mmh2o) = p(inh2o) ÷ 0.03937007874015748
Examples
Example #1: Convert 1 inh2o to mmh2o
1 inh2o = 1 inh2o × (249.08891/9.80665) mmh2o = 25.4 mmh2o
1 inh2o = 1 inh2o ÷ 0.03937007874015748 = 25.4 mmh2o
1 inh2o × (249.08891/9.80665) = 25.400000 mmh2o
Example #2: Convert 10 inh2o to mmh2o
10 inh2o = 10 inh2o × (249.08891/9.80665) mmh2o = 254 mmh2o
10 inh2o = 10 inh2o ÷ 0.03937007874015748 = 254 mmh2o
10 inh2o × (249.08891/9.80665) = 254.000000 mmh2o
Summary
To convert inH2O to mmH2O, multiply the value in inh2o by (249.08891 Pa per inh2o) / (9.80665 Pa per mmh2o). Equivalently: value_mmh2o = value_inh2o × (249.08891 / 9.80665). Numerically, 1 inh2o equals 25.400000000000002 mmh2o.
Relationship context
Both inH2O and mmH2O are converted by fixed multiples of the pascal. Multiplying by (Pa per inh2o) ÷ (Pa per mmh2o) gives the same result as passing through pascal, keeping bar, atm, PSI, kPa, hPa, torr, and mmHg consistent on the hub.
Conversion tables
| inH2O (inh2o) | mmH2O (mmh2o) |
|---|---|
| 0.1 | 2.54 |
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 6 | 152.4 |
| 7 | 177.8 |
| 8 | 203.2 |
| 9 | 228.6 |
| inH2O (inh2o) | mmH2O (mmh2o) |
|---|---|
| 10 | 254 |
| 20 | 508 |
| 30 | 762 |
| 40 | 1,016 |
| 50 | 1,270 |
| 60 | 1,524 |
| 70 | 1,778 |
| 80 | 2,032 |
| 90 | 2,286 |
| 100 | 2,540 |