Example data table
| Scenario | Inputs | Output (target) |
|---|---|---|
| 18" spillway, medium sheet | Weir 18 in • Lift 4 ft • Pipe 20 ft @ 1 in • 2 elbows • Safety 15% | ≈ 3,105 GPH @ ~4.5 ft TDH |
| Small fountain jet | Nozzle 0.5 in • Jet 3 ft • Lift 2 ft • Short piping • Safety 10% | ≈ 2,700 GPH @ ~2.1 ft TDH |
| Turnover-focused pond | Volume 500 gal • Turnover 2 hr • Lift 3 ft • Pipe 30 ft @ 1.25 in | ≈ 288 GPH @ ~3.2 ft TDH |
Formula used
A practical rule is used for sheet thickness:
- Gentle: GPH = width(in) × 100
- Medium: GPH = width(in) × 150
- Heavy: GPH = width(in) × 200
Head loss for water is estimated as:
Where L is feet, Q is GPM, d is inches, and C depends on material.
Total dynamic head is TDH = lift + hf. The required flow is the maximum of spillway, fountain, and turnover needs, then increased by the chosen safety margin.
How to use this calculator
- Select your units and the feature type you are designing.
- Enter spillway width or nozzle size and desired jet height.
- Optionally add pond volume and a turnover target in hours.
- Measure vertical lift, then add pipe length, diameter, and fittings.
- Click Calculate Flow to see the target flow at TDH.
- Choose a pump that delivers the target flow at that head.
Flow targets for waterfalls and spillways
For sheet-style water features, flow is driven by weir width and the visual thickness you want. A gentle sheet suits quiet patios, while a heavier sheet masks pump noise and creates stronger sound. This calculator uses common planning ranges per inch of spillway to produce a realistic starting flow, then adds a safety margin for real-world losses.
Fountain jets and nozzle sizing
Jet height depends on velocity at the nozzle, so small diameter changes matter. The nozzle estimate scales with nozzle area and the square-root of target height, which mirrors how pressure needs rise as you push water higher. Use this to compare alternate nozzles before buying a pump or changing plumbing.
Turnover rate and water quality
Turnover is how quickly the pond volume cycles through filtration. Faster turnover helps clarity in warm weather and heavy feeding, while slower turnover can be acceptable for lightly stocked ponds. Enter volume and desired hours to ensure circulation demand is not overlooked when designing a show feature.
Head loss: lift, pipe, and fittings
A pump must deliver flow at total dynamic head, not at zero head. Vertical lift is only part of the story; pipe friction and fittings reduce output too. The calculator estimates friction using the Hazen–Williams method and converts elbows, tees, and valves into equivalent length, so you can see how layout choices affect head.
Choosing a pump from performance curves
Use the result as a shopping target: find a pump curve that meets the recommended flow at the computed head. If the curve falls short, increase pipe diameter, shorten runs, reduce restrictive fittings, or select a higher-capacity pump. Keep some adjustment range so seasonal cleaning and biofilm do not degrade performance. Match electrical load to a protected circuit, and confirm the pump’s solids handling if leaves are present. For formal spillways, consider a valve for fine tuning. Record your final settings and export the report for maintenance notes.