Updated Apr 9, 2026 — Reviewed by Sino-Inst Engineering Team
In fluid mechanics, pressure splits into three components: static pressure, dynamic pressure, and total pressure. These are not three separate forces — they are three ways of describing the energy state of a moving fluid. Bernoulli\’s principle ties them together in one equation. If you work with HVAC ducts, pipeline flow measurement, or aerospace systems, you deal with these three pressures every day. This guide covers definitions, formulas, how to measure each one, and which instruments to use.
Contents
- What Is Static Pressure
- What Is Dynamic Pressure
- What Is Total Pressure (Bernoulli\’s Equation)
- Quick Comparison Table
- How to Measure Static, Dynamic, and Total Pressure
- Industrial Applications
- Featured Pressure Instruments
- Frequently Asked Questions
What Is Static Pressure
Static pressure is the pressure exerted by a fluid when you ignore its motion. Think of it as the “stored energy” component. In a sealed tank with no flow, all pressure is static. In a moving pipe, static pressure acts perpendicular to the flow direction — it pushes equally on all sides of the pipe wall.
The formula is straightforward. For a fluid column:
Pstatic = ρ × g × h
Where ρ is fluid density (kg/m³), g is gravitational acceleration (9.81 m/s²), and h is the fluid column height (m). In a 10-meter water column, static pressure at the bottom is approximately 98.1 kPa (about 1 atm).
In HVAC systems, duct static pressure typically ranges from 0.5 to 2.0 inches of water column (125–500 Pa). Too high means restricted airflow. Too low means the fan cannot push air to remote zones. A pressure transmitter mounted on the duct wall with a perpendicular tap measures static pressure directly.
What Is Dynamic Pressure
Dynamic pressure represents the kinetic energy of a moving fluid per unit volume. It only exists when the fluid is in motion. Stop the flow, and dynamic pressure drops to zero.
The formula:
Pdynamic = ½ × ρ × v²
Where ρ is fluid density (kg/m³) and v is flow velocity (m/s). Note the squared relationship — doubling the velocity quadruples the dynamic pressure. This is why high-velocity flows create much larger forces than low-velocity ones.
Practical example: air at standard conditions (ρ = 1.225 kg/m³) moving at 20 m/s produces a dynamic pressure of about 245 Pa. At 40 m/s, it jumps to 980 Pa. This matters in wind tunnel testing and in sizing pressure sensors for industrial applications.
Dynamic pressure is always positive. It has direction — it acts along the flow axis. A pressure tap flush with the pipe wall does not sense dynamic pressure. You need a probe facing directly into the flow, like a pitot tube.
What Is Total Pressure (Bernoulli’s Equation)
Total pressure (also called stagnation pressure) is the sum of static and dynamic pressure. Bernoulli’s equation for incompressible flow along a streamline states:
Ptotal = Pstatic + ½ρv²
The total pressure remains constant along a streamline in ideal (inviscid, incompressible) flow. When fluid slows down, dynamic pressure converts to static pressure. When it speeds up, static converts to dynamic. The total stays the same.
This is the principle behind every pitot tube measurement. A pitot tube has two ports: one facing into the flow (measures total pressure) and one perpendicular to the flow (measures static pressure). The difference between them is dynamic pressure, from which you calculate velocity:
v = √(2 × (Ptotal – Pstatic) / ρ)
In real systems with friction and turbulence, total pressure decreases along the flow path. The relationship between flow rate and pressure becomes more complex, and you must account for pressure losses in pipe fittings, valves, and elbows.
Quick Comparison Table
| Property | Static Pressure | Dynamic Pressure | Total Pressure |
|---|---|---|---|
| Definition | Pressure from random molecular motion | Pressure from bulk fluid velocity | Sum of static + dynamic |
| Formula | Ps = ρgh (column) or measured directly | Pd = ½ρv² | Pt = Ps + ½ρv² |
| Direction | Acts in all directions (isotropic) | Acts along flow direction only | Measured facing into flow |
| At zero flow | Equals total pressure | Zero | Equals static pressure |
| Sign | Positive or negative (vacuum) | Always positive | Positive or negative |
| Measurement | Wall tap perpendicular to flow | Calculated from total minus static | Pitot tube facing into flow |
| Unit | Pa, psi, inH₂O | Pa, psi, inH₂O | Pa, psi, inH₂O |
How to Measure Static, Dynamic, and Total Pressure
Static Pressure Measurement
Drill a small hole (typically 1–3 mm) perpendicular to the pipe wall. Connect a pressure transmitter or manometer. The tap must be flush with the inner wall — any burr or protrusion will cause measurement errors. In round ducts, place the tap at the 3 o’clock or 9 o’clock position to avoid effects from gravity (condensate) or buoyancy.
Total Pressure Measurement
Insert a pitot tube with its open end facing directly upstream. The stagnation point at the tube opening brings the fluid velocity to zero, converting all kinetic energy to pressure. This reading is total pressure. For accurate results, align the tube within ±5° of the flow direction.
Dynamic Pressure (Velocity Pressure)
Dynamic pressure is not measured directly. Instead, connect a differential pressure transmitter between the total pressure port and the static pressure port. The DP reading equals dynamic pressure. From this, calculate flow velocity using the formula above.
For HVAC duct traversals, averaging pitot tubes (like an Annubar) provide a more representative velocity reading across the duct cross-section. Single-point pitot readings can miss the velocity profile and understate or overstate average flow. Follow the log-linear or equal-area traverse method per ASHRAE standards for best accuracy.
Industrial Applications
HVAC systems: Static pressure monitoring at key duct locations ensures the air handling unit delivers correct airflow. Excessive static pressure indicates blocked filters or closed dampers. Building automation systems use duct static pressure sensors as feedback for variable-frequency drives on supply fans.
Pipeline flow measurement: Differential pressure flow meters (orifice plates, Venturi tubes, flow nozzles) work by creating a pressure drop. The upstream and downstream straight pipe requirements ensure a stable velocity profile for accurate DP readings. The measured DP relates to flow rate through a square-root relationship.
Aerospace: Aircraft airspeed indicators use pitot-static systems. The pitot port measures total pressure (ram air). The static port measures ambient static pressure. The difference gives dynamic pressure, which converts to indicated airspeed. At higher speeds (above Mach 0.3), compressibility effects require corrections beyond Bernoulli’s incompressible equation.
Clean rooms and labs: Differential static pressure between rooms ensures contamination control. Positive-pressure rooms prevent outside air from entering. Negative-pressure isolation rooms prevent pathogens from escaping. Monitoring requires sensitive low-range pressure transmitters with 0–250 Pa or 0–500 Pa ranges.
Featured Pressure Instruments
Sino-Inst manufactures pressure transmitters suitable for static, differential, and dynamic pressure measurement across industrial applications.
Gauge Pressure Transmitter
4-20mA / HART | 0–100 kPa to 0–60 MPa | ±0.075% FS
Differential Pressure Transmitter
4-20mA / HART | 0–6 kPa to 0–10 MPa | ±0.075% FS
SI-503K Gas Pressure Sensor
0–5 kPa to 0–200 kPa | 4-20mA | Air & gas applications
Frequently Asked Questions
What is the difference between static and dynamic pressure?
Static pressure exists whether the fluid moves or not — it comes from the weight and random molecular motion of the fluid. Dynamic pressure only exists when the fluid is in motion and represents the kinetic energy of that motion. Static pressure acts in all directions; dynamic pressure acts along the flow direction only.
Can dynamic pressure be negative?
No. Dynamic pressure equals ½ρv², and both density (ρ) and velocity squared (v²) are always positive. Dynamic pressure is zero when there is no flow and positive for any nonzero velocity, regardless of flow direction.
How does a pitot tube measure total pressure?
A pitot tube has an open end facing directly into the flow. At this stagnation point, the fluid velocity drops to zero, and all kinetic energy converts to pressure energy. The pressure reading at this point equals the total pressure (static + dynamic). A second port perpendicular to flow measures static pressure. The difference is dynamic pressure.
What is stagnation pressure?
Stagnation pressure is another name for total pressure. It is the pressure at a point where the fluid velocity has been brought to zero isentropically (without heat transfer or friction losses). In practice, the tip of a pitot tube approximates a stagnation point.
What instrument measures static pressure in HVAC ducts?
A duct static pressure sensor or low-range differential pressure transmitter connected to a wall tap. The tap should be drilled perpendicular to the duct wall, with no burrs. Common sensing ranges are 0–250 Pa, 0–500 Pa, or 0–1000 Pa depending on the system. The sensor’s reference port is left open to atmosphere or connected to a clean reference point.
Does Bernoulli’s equation apply to compressible flow?
The standard Bernoulli equation (Ptotal = Pstatic + ½ρv²) applies only to incompressible, inviscid, steady flow along a streamline. For compressible flow (gas at Mach > 0.3), you need the compressible form that accounts for density changes. For most industrial piping and HVAC applications, the incompressible form is accurate enough because flow velocities are well below Mach 0.3.
Need help selecting the right pressure instrument for your static, dynamic, or differential pressure measurement? Our engineering team can recommend the best sensor type, range, and output for your application.
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Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.