Civil Engineering Unit Conversions
Plans, reports and product data mix units: flows in cfs, gpm and MGD, loads in kips and pounds per square foot, bearing pressure in tsf. This table lists the conversions that come up most often on US site, utility and structural work. Factors are derived from the exact definitions of the inch, the pound-force and the US gallon.
| Quantity | From | Equals | Unit |
|---|---|---|---|
| Length | 1 inch | 25.4 | mm |
| Length | 1 foot | 0.3048 | m |
| Length | 1 mile | 5,280 | ft |
| Area | 1 acre | 43,560 | ft2 |
| Area | 1 acre | 0.404686 | hectare |
| Area | 1 square foot | 0.092903 | m2 |
| Volume | 1 cubic yard | 27 | ft3 |
| Volume | 1 cubic yard | 0.764555 | m3 |
| Volume | 1 cubic foot | 7.48052 | US gal |
| Volume | 1 acre-foot | 43,560 | ft3 |
| Volume | 1 acre-foot | 325,851 | US gal |
| Flow | 1 cfs | 448.831 | gpm |
| Flow | 1 MGD | 1.54723 | cfs |
| Flow | 1 MGD | 694.444 | gpm |
| Force | 1 lbf | 4.44822 | N |
| Force | 1 kip | 4.44822 | kN |
| Force | 1 ton (short) | 2,000 | lb |
| Stress and pressure | 1 psi | 6.89476 | kPa |
| Stress and pressure | 1 ksi | 6.89476 | MPa |
| Stress and pressure | 1 psf | 47.8803 | Pa |
| Stress and pressure | 1 ksf | 47.8803 | kPa |
| Stress and pressure | 1 tsf | 2,000 | psf |
| Stress and pressure | 1 ft of water head | 0.4335 | psi |
| Unit weight | 1 lb/ft3 | 0.157087 | kN/m3 |
Notes
- Exact definitions: 1 in = 2.54 cm; 1 US gallon = 231 in3; 1 lbf = 4.4482216152605 N.
- The water head conversion uses fresh water at about 62.4 lb/ft3 (62.4 / 144 = 0.4335 psi per foot); conversely 1 psi is about 2.31 ft of water.
- MGD means million gallons per day.
- Values are rounded to six significant figures.
Frequently asked questions
How many gallons per minute is 1 cfs?
1 cubic foot per second is 448.831 gallons per minute.
How many cfs is 1 MGD?
1 million gallons per day is 1.54723 cfs, or about 694.4 gpm.
How do I convert feet of water to psi?
Multiply feet of fresh water by 0.4335. A 100 foot water tower produces about 43.4 psi at its base.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B
- NIST Handbook 44, Appendix C, General Tables of Units of Measurement
More reference tables
Lumber Nominal vs Actual SizesMinimum Concrete Cover for Rebar (ACI 318)OSHA Trench Soil Types and Maximum Allowable SlopesPVC SDR 35 Sewer Pipe Sizes (ASTM D3034)Presumptive Soil Bearing Values (IBC Table 1806.2)Runoff Coefficients (C) for the Rational MethodSlope Ratio to Percent and DegreesUS Rebar Sizes, Areas and WeightsUnit Weights of Common Construction Materials
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