--- title: How to Calculate TDH for Dewatering Pump Selection date: 2026-08-12T00:30:00Z modified: 2026-08-31T06:54:58Z permalink: "https://www.defucc.com/blog/buying-guide/total-dynamic-head-dewatering-pump/" type: post status: publish excerpt: "" wpid: 2852 categories: - buying guide featured_image: "https://www.defucc.com/wp-content/uploads/2026/08/image-8.webp" featured_image_alt: How to Calculate TDH for Dewatering Pump Selection timestamp: 2026-08-31T06:54:58Z tags: - buying guide --- ## **Quick Answer:** Total dynamic head (TDH) = static head + friction head loss + pressure head. Measure static head from the lowest expected water level to the discharge point, add losses through the pipe, hose, and fittings, then add any discharge backpressure. If water discharges freely to atmosphere, pressure head is zero. ## **What Is Total Dynamic Head?** Total dynamic head is the total resistance a [dewatering pump](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/page/types-of-dewatering-pumps.md) must overcome to move water from the source to the discharge point. You typically measure it in feet or meters of head. The total dynamic head formula is: **TDH = Static Head + Friction Head Loss + Pressure Head** Where the static head is the vertical distance required for the water to be lifted, and pressure head is any pressure that has to be overcome by the pump at the discharge point. Friction head is the resistance formed as the water moves through the fittings and pipe. ## **How Do You Calculate Static Head?** For a surface dewatering pump installed above the water source, add the suction static lift and discharge static head: **Total Static Head = Suction Static Lift + Discharge Static Head** Assuming the pump is sitting 10 feet above the water while the discharge point is 50 feet above the pump, the static head comes out to 60 feet. As you measure this, make sure to consider the lowest expected water level. The vertical lift increases and the water level drops as a sump, excavation, or pit drains. Calculating from the starting water level usually means underestimating the static head your pump might need to overcome. Measure the elevation difference from the lowest expected water level to the discharge point. The extra static head doesn’t account for the pump’s installation depth below the water surface. ## **How Do You Calculate Friction Head Loss?** Water loses energy as it moves through a pipe or hose. In a pump head calculation, that resistance is counted as friction head loss. Friction loss depends on the line’s internal diameter, total length, material or roughness, and how quickly water moves through it. A longer or narrower line generally creates more loss. Elbows, check valves, foot valves, strainers, and reducers add resistance too. An easy way to account for them is to convert each fitting into an equivalent length of straight pipe. Add those lengths to the actual pipe run, then calculate friction loss using the new total. Suppose 400 feet of pipe has fittings equal to another 119 feet of straight pipe. Your friction calculation would use a total equivalent length of 519 feet rather than 400 feet. Don’t use a generic friction percentage. Friction loss changes with the line you’re using and how you’re running it, so calculate it for the actual setup. ## **When Do You Add Pressure Head?** Pressure head matters when the pump discharges into something that already has pressure, such as a pressurized manifold or closed system. For water, you can convert discharge pressure into head with these relationships: **Head (ft) = Pressure (psi) × 2.31** **Head (m) = Pressure (bar) × 10.2** These conversions work for clean water with a specific gravity of about 1.0. If the hose discharges freely into an open ditch, tank, or another point exposed to the atmosphere, the discharge pressure head is zero. That means many basic construction and [mine dewatering](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/page/mine-dewatering-pump-manufacturer.md) setups only need static head and friction loss in the final TDH total. ## **What Does a TDH Calculation Look Like in a Dewatering Job?** Assume there is an excavation with 400 feet of 4-inch pipe and 80 feet of static head, and you’re dewatering it. There’s also an extra 119 feet of pipe length from the elbows and valves. That is 519 feet of equivalent pipe, so if the friction-loss rate is 4.5 feet per 100 feet, the friction head becomes: **519 ÷ 100 × 4.5 = 23.36 feet** The line discharges to the atmosphere, so the pressure head is 0 feet. The TDH calculation is: **TDH = 80 + 23.36 + 0 = 103.36 feet** As such, the pump has to overcome about 103 feet of overall head in this scenario. But instead of applying this number to every job, recalculate it if the fittings, discharge pressure, lowest water level, or hose route changes. MP Series Vacuum Assisted Dry Priming Slurry Dewatering Pump High-performance solution for the most demanding dewatering tasks in mining, offering unmatched efficiency and reliability. [Explore Mine-Dewatering Pumps](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/page/mine-dewatering-pump-manufacturer.md) [ ![DEFUC IHF Chemical Centrifugal Pump](https://www.defucc.com/wp-content/uploads/2025/05/MP-800x800.jpg) ](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/page/mine-dewatering-pump-manufacturer.md) ## **How Can You Check Your TDH Before Using It?** Friction loss is usually the tedious part to work out by hand. [DEFU’s pump head calculator](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/page/pump-head-calculator.md) can help with that part using the vertical lift, line length, internal diameter, pipe material, and operating flow. Use measurements from the actual job site, including the lowest expected water level and actual discharge-line dimensions. Account for the fittings too. With DEFU’s pump head data tested in accordance with [ISO 9906](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/post/the-importance-of-iso-9906-certification-in-pump-selection.md), you get standardized hydraulic test data rather than relying only on nominal head figures when checking your TDH requirement. [Get Free Quote](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/page/contact.md) Welcome to Our Blog! Professional Dewatering Pump Manufacturer Written by the Engineering & Solutions Team at WENZHOU DEFU MACHINERY CO., LTD. Backed by 3 manufacturing bases and over 10 years of expertise as a leading dewatering pump manufacturer, our team is dedicated to sharing practical dewatering pump insights and engineered fluid handling solutions for global projects. [ Contact Us → ](https://www.defucc.com/wp-content/uploads/wp-mfa-exports/page/contact.md) ![WENZHOU DEFU MACHINERY CO., LTD. - Dewatering Pump Manufacturer](https://defucc.b-cdn.net/wp-content/uploads/2025/06/2-1-1--768x534.jpg)