Feet of head is a way of measuring how much energy a pump can deliver to a fluid, expressed as the height (in feet) that the pump could push a column of that fluid straight up. A pump rated at 100 feet of head, for example, could theoretically lift water 100 feet vertically. It’s the standard unit used across the pump industry instead of pressure because it stays constant regardless of what liquid you’re pumping.
Why Feet Instead of PSI
This is the part that trips most people up. Pressure (PSI) changes depending on how heavy the liquid is, but head in feet does not. A pump that produces 100 feet of head will always produce 100 feet of head whether it’s moving water, gasoline, or saltwater. The pressure at the bottom of that 100-foot column, however, will be different for each liquid because they have different densities.
For water at standard conditions, one foot of head equals 0.433 PSI. So a pump producing 100 feet of head generates about 43.3 PSI when pumping water. If you’re pumping a heavier fluid with a specific gravity of 1.2, that same 100 feet of head produces roughly 52 PSI. The pump is doing the same work, but the heavier fluid creates more pressure per foot of height. This is why the industry settled on feet of head as the universal measure: it describes the pump’s capability without tying it to a specific fluid.
To convert between head and pressure for any fluid, the relationship is: Head (feet) = 2.31 × PSI ÷ specific gravity. So as specific gravity goes up, you actually need fewer feet of head to reach the same pressure rating.
What Makes Up Total Dynamic Head
When you’re sizing a pump for a real system, the number that matters is Total Dynamic Head (TDH). This is the total amount of work your pump needs to do, and it combines several components into one number measured in feet.
Static head is the simplest piece: the vertical distance the fluid needs to travel. If your pump sits at ground level and pushes water to a tank 50 feet above it, you have 50 feet of static discharge head. If the water source sits below the pump, that vertical distance down to the source is your static suction lift. Add the two together and you get total static head.
Friction head accounts for the energy lost as fluid drags against pipe walls, squeezes through valves, and changes direction at elbows. Every foot of pipe, every fitting, and every valve steals a little energy from the flow. Friction losses depend on several factors: pipe length, pipe diameter, flow velocity, and how rough the inside of the pipe is. Longer pipes, smaller diameters, faster flow, and rougher interior surfaces all increase friction losses. The relationship is dramatic in some cases. Friction loss increases with the square of velocity, so doubling the flow speed roughly quadruples the friction losses.
The full formula is straightforward:
TDH = Static Head + Friction Losses + Miscellaneous Losses
Miscellaneous losses cover fittings like elbows, tee joints, check valves, filters, and heaters. Engineers often express these as “equivalent length,” converting each fitting into the length of straight pipe that would cause the same amount of friction loss. A 90-degree elbow, for instance, might be equivalent to several feet of straight pipe depending on its size.
How Head Appears on a Pump Curve
Every centrifugal pump comes with a performance curve that plots head against flow rate, typically in gallons per minute (GPM). The core relationship is an inverse one: a pump can deliver high flow at low head, or low flow at high head, but not both at once. As you ask a pump to push against more resistance (more feet of head), the flow rate drops.
At one extreme of the curve is the shut-off head. This is the maximum head a pump can produce, and it occurs at zero flow. Imagine a pump connected to a vertical pipe with no outlet. The water rises until it can’t overcome gravity anymore and stops. That maximum height is the shut-off head. At the other extreme, when there’s almost no resistance in the system, the pump delivers its maximum flow rate but very little head.
When selecting a pump, you find your system’s TDH on the vertical axis and your required flow rate on the horizontal axis. The intersection point tells you whether a given pump can handle the job. For instance, a pump with an 8.5-inch impeller might deliver about 42 GPM against 120 feet of head at roughly 73% efficiency. Move to a different point on that curve and all three numbers change.
Net Positive Suction Head
There’s one more “head” term you’ll encounter when working with pumps: Net Positive Suction Head, or NPSH. This measures the pressure available at the pump’s inlet, and it exists to prevent cavitation.
Pumps work by creating low pressure at the inlet to draw fluid in. If that inlet pressure drops too low, the fluid essentially starts to boil, forming tiny vapor bubbles. Those bubbles then collapse violently inside the pump, producing a sound like gravel rattling in a concrete mixer. More importantly, each collapsing bubble blasts a tiny pit into the pump’s internal surfaces, causing permanent damage over time.
Two values matter here. NPSH available (NPSHa) is the actual pressure your system provides at the pump inlet, determined by your piping layout, fluid temperature, and elevation. NPSH required (NPSHr) is the minimum inlet pressure the pump needs to operate without forming bubbles. The available value must always exceed the required value. A common guideline is to keep NPSHa higher than NPSHr by at least 5 feet or 10% of NPSHa, whichever is greater. So if your pump requires 10 feet of NPSH, your system should provide at least 15 feet at the inlet.
How Fluid Properties Change the Picture
A pump’s head rating stays the same no matter what liquid it moves, but the power needed to move that liquid does not. The formula for pump work is flow rate (GPM) × fluid density × head, and the result is measured in foot-pounds per minute. Pump a fluid that’s 20% heavier than water, and you need 20% more power to achieve the same flow and head.
Specific gravity also changes how you convert between head and pressure. If you need a system to maintain 35 PSI and you’re pumping a fluid with a specific gravity of 1.05, you’ll actually need slightly less head than you would for pure water at the same pressure. The heavier fluid generates more pressure per foot of height, so fewer feet get you to the same PSI. This distinction matters when you’re sizing a pump for chemicals, brines, or slurries rather than plain water.
Reducing Head Requirements in Your System
Since TDH directly determines what pump you need (and how much energy it consumes), reducing head requirements can save money on both equipment and electricity. Static head is fixed by your layout, but friction losses are within your control. Using larger-diameter pipes is one of the most effective changes, since head loss is inversely proportional to pipe diameter. Shorter pipe runs, fewer elbows, and smoother pipe materials (like PVC versus corrugated steel) all cut friction head. Keeping valves fully open rather than partially throttled eliminates unnecessary resistance. Even replacing sharp 90-degree elbows with long-radius bends makes a measurable difference in systems with high flow rates.