Water operator math tutorial
Pressure and Head
Convert feet of head to pounds per square inch.
A column of water exerts 0.433 psi for every foot of height. That is how an elevated tank's height becomes distribution system pressure.
The reverse conversion uses 2.31 feet of head per psi. Pick the factor that matches the direction you are converting.
The formula
pressure (psi) = head (ft) × 0.433 psi/ft
| Variable | Unit |
|---|---|
| Head | ft |
| Result: Pressure | psi |
Conversion factors used: 0.433 psi per foot of head; 2.31 ft of head per psi.
Applies to: Water Distribution, Water Treatment.
Common exam tip: Quick check: 100 ft is about 43 psi. Your answer should be in that neighborhood.
Calculator
Pressure
43.3 psi
- 1. 100 ft × 0.433 psi/ft = 43.3 psi
For instructional use. Results assume the standard conversion factors shown on this page. Actual field calculations may need chemical strength, density, temperature, and other adjustments, so check your plant’s procedures.
Worked examples
Example 1
An elevated tank sits 100 ft above a service connection.
- 100 ft × 0.433 psi/ft = 43.3 psi
Answer: 43.3 psi
Example 2
A reservoir is 230 ft above a pressure gauge.
- 230 ft × 0.433 psi/ft = 99.59 psi
Answer: 99.59 psi
Common mistakes
Wrong result: 231 psi
using 2.31, the feet-per-psi factor, in the wrong direction
Wrong result: 230.95 psi
dividing by 0.433 instead of multiplying
Practice questions
1. 80 ft of head. What is the pressure in psi?
- A34.64 psi
- B184.8 psi
- C184.76 psi
- D346.4 psi
Show answer and explanation
Correct answer: A. 80 ft × 0.433 psi/ft = 34.64 psi Answer: 34.64 psi. A common slip is using 2.31, the feet-per-psi factor, in the wrong direction, which gives 184.8 psi.
2. 120 ft of head. What is the pressure in psi?
- A277.2 psi
- B51.96 psi
- C277.14 psi
- D519.6 psi
Show answer and explanation
Correct answer: B. 120 ft × 0.433 psi/ft = 51.96 psi Answer: 51.96 psi. A common slip is using 2.31, the feet-per-psi factor, in the wrong direction, which gives 277.2 psi.
3. 310 ft of head. What is the pressure in psi?
- A716.1 psi
- B715.94 psi
- C134.23 psi
- D1,342.3 psi
Show answer and explanation
Correct answer: C. 310 ft × 0.433 psi/ft = 134.23 psi Answer: 134.23 psi. A common slip is using 2.31, the feet-per-psi factor, in the wrong direction, which gives 716.1 psi.
Where this formula applies
This calculation can appear in the disciplines below. Exact exam coverage depends on your state, certification level, and official exam outline.
Water Distribution
Water Treatment
Study guides
Keep going with the full guide
Water Operator Math Made Simple walks through operator math step by step and includes printable references plus a full practice exam.
Water Operator Math Made Simple
A Step-by-Step Guide to the Math Every Water Operator Needs to Know