Calculate Total Dynamic Head (TDH) for your pool plumbing system. Use gauge readings or pipe specifications to determine system resistance and optimize pump performance.
Choose your calculation method below and get instant TDH results with pump sizing recommendations.
Read on filter or return side
Read on suction side of pump
Total suction + return length
Count all 90° turns
Count all 45° turns
Height from water to equipment
0 ft
Low Resistance
Your system resistance is within normal range.
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Total Dynamic Head (TDH) is the total resistance a pool pump must overcome to circulate water through the plumbing system. Measured in feet of head, TDH accounts for every source of friction and resistance in your pool's plumbing: pipe friction, elevation changes, filter resistance, fittings, and valves. Understanding TDH is essential for selecting the right pump, optimizing energy efficiency, and diagnosing flow problems.
Think of TDH as the "difficulty score" for your plumbing system. A low TDH means water flows easily; a high TDH means the pump has to work harder to push water through the system. Every pool has a unique TDH based on its plumbing layout, pipe sizes, equipment, and elevation.
TDH is the single most important factor in choosing the right pool pump. Every pump has a performance curve that shows how much water (GPM) it can move at different levels of resistance (TDH). If your TDH is too high for your pump, flow drops dramatically and the pump works harder, wastes energy, and wears out faster.
The gauge method is the fastest and most accurate way to measure TDH on an existing system. You need two readings:
The pressure gauge is typically mounted on or near the filter. It reads in PSI (pounds per square inch) and tells you how much resistance the pump is pushing against on the return side. A typical clean-filter reading is 10-20 PSI. As the filter gets dirty, this number rises. When it's 8-10 PSI above the clean reading, it's time to clean or backwash the filter.
The vacuum gauge is mounted on the suction side of the pump, before the impeller. It reads in inches of mercury (inHg) and tells you how hard the pump is pulling water from the pool. A typical reading is 5-15 inHg. High vacuum readings (above 15 inHg) indicate a restriction on the suction side: clogged skimmer basket, blocked main drain, undersized suction pipe, or air leak.
To convert gauge readings to TDH:
For example, if your pressure gauge reads 18 PSI and your vacuum gauge reads 10 inHg: TDH = (18 × 2.31) + (10 × 1.13) = 41.6 + 11.3 = 52.9 feet of head.
This calculator offers both approaches, and each has its strengths:
Pipe diameter has an enormous effect on friction loss and TDH. Friction loss follows roughly an inverse-fifth-power relationship with pipe diameter, which means small increases in pipe size produce dramatic reductions in friction:
If your TDH is too high, upgrading from 1.5" to 2" pipe on the suction side alone can cut total friction loss by more than half. This is one of the most cost-effective upgrades for older pool systems.
A TDH above 60 feet is too high for most residential pool pumps. The pump is working extremely hard and flow rate is severely reduced. Common causes include undersized pipe (1.5" on long runs), excessive fittings, dirty filter, or restrictive valves.
Solutions: Upsize pipe to 2" or larger, reduce the number of elbows, clean or replace the filter, open all valves fully, or upgrade to a pump designed for high-head applications.
This range is workable but not ideal. A single-speed pump can handle it, but energy costs will be high. A variable-speed pump may not be able to run at its lowest (most efficient) speeds because flow would drop too much.
Solutions: Focus on the biggest contributors. If filter resistance is high, clean or replace media. If you have many elbows, consider replumbing with sweep 90s or reducing fitting count. A VS pump at medium speed (2000-2500 RPM) is a good match for this range.
If TDH reads low but flow seems weak, the problem is likely not plumbing resistance. Check for an air leak on the suction side, a worn impeller, a clogged impeller (debris wrapped around it), or a pump that's simply too small for the pool volume.
A vacuum reading above 15 inHg indicates a suction-side restriction. Check the skimmer basket, pump strainer basket, main drain cover, and suction-side valves. Also inspect for collapsed or kinked flexible hose on the suction line.
Most residential pools should aim for a TDH between 30-50 feet of head. Below 30 ft is excellent and allows a variable-speed pump to run very efficiently at low RPMs. Between 40-50 ft is typical for standard installations. Above 50 ft starts to become problematic, and above 60 ft usually indicates a plumbing issue that needs to be addressed.
Yes. TDH increases as the filter gets dirty (the biggest variable), as pipes age and develop mineral buildup inside, and as valves corrode. It can also change seasonally if you adjust valve positions for different suction sources (skimmer vs. main drain). This is why the gauge method gives you a real-time snapshot, while the calculation method gives you a baseline estimate.
A variable-speed pump adjusts its RPM to match the system's needs. At lower speeds, it produces less flow but uses dramatically less energy (energy consumption follows a cubic relationship with speed). On a low-TDH system, a VS pump can run at 1200-1500 RPM for daily filtration, using as little as 200-400 watts. On a high-TDH system, the pump needs higher RPMs to maintain adequate flow, which reduces the energy savings.
Yes, several options can reduce TDH without a full replumb. Keep filters clean, remove unnecessary valves or fittings, ensure all valves are fully open, replace standard 90-degree elbows with sweep elbows (lower friction), and make sure pump and skimmer baskets are clean. Upgrading just the suction-side piping from 1.5" to 2" is also a relatively easy partial upgrade that can make a big difference.
Static head is simply the vertical distance (elevation change) between the water surface and the highest point in the plumbing. It's only one component of TDH. Total Dynamic Head includes static head plus all friction losses from pipe, fittings, filter, heater, and any other equipment. Static head is constant regardless of flow rate, while friction losses increase as flow rate increases.
Check the pump's performance curve, available from the manufacturer. Find your TDH on the horizontal axis and read the corresponding GPM on the vertical axis. For proper pool filtration, you need enough GPM to turn over your pool volume at least once every 8 hours (once every 6 hours is better). For example, a 20,000-gallon pool needs at least 42 GPM (20,000 / 8 hours / 60 minutes). If your pump can deliver that flow at your TDH, it's properly sized.
For more information on pool plumbing, pump sizing, and system optimization, explore our other free tools:
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