Following is a set of useful calculators in Imperial and Metric systems.
Scroll down or click any of the below links.
Water Volume Calculator
Waterfall Flow Calculator
Water Rotations Calculator
Pipe Sizing Calculator
Evaporation Loss Calculator
Overflow Calculator
Water-in-Transit Calculator

All sections provide comments related to the nature of each calculation.
If you prefer to skip these comments and go directly to the calculation page click here.

If you need to convert some units between the METRIC and IMPERIAL systems or change some units (i.e. US Gallons to ft³), LASquare Unit Converters located here may come very useful.

Water Volume Calculator

This calculator allows you to estimate the volume of water in your pool(s). This calculation is based on the existing (measured) or designed  pool(s) area and pool(s) depth. The calculated value is provided in US Gallons, cubic feet, liters and cubic meters. You may find this information quite practical as in your region (i.e. Canada) you may be dealing with both (imperial and metric) standards at the same time.

If you have several connected pools or your pool depth varies, you may need to separately calculate each pool or its area, and combine the calculated values to obtain the total volume of water in your system.

If a pool with a sloping floor has a simple, geometric shape you may be able to calculate an average depth of water and use this value to get the approximate volume of water in the pools.

In ponds with very irregular shape and/or water depth (i.e. natural pond with few islands) you may be able to approximate the pool area and/or its depth and calculate the water volume based on your best guess. However, if you require a very accurate calculation you may need to obtain a proper survey completed by a surveyor, before you can calculate an accurate water volume.

Keep in mind that not all water features require a very accurate calculation of water volume. For example, if you are dealing with a natural pond with seasonal changes of water depth, knowing only an approximate pool area and its water volume may be sufficient to estimate the make-up water requirements or water rotations frequency.

Knowing the volume of water in your water feature is necessary to evaluate its weight, which may be critical for the structural or geo-technical coordination of the project. Also, considering the constantly growing value of fresh water resources, the water volume requirements for filling the pool(s) may be quite important. If the pool is intended for a rainwater harvesting project, knowing its capacity is also critical.

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Waterfall Flow Calculator

This calculator allows you to estimate the waterfall flow, which is the water flow required to feed your waterfall of a given weir length and the desired waterfall thickness (water depth at the edge of the weir.)

Remember that weir shape, its construction material and levelness of installation will visually affect the waterfall. If the weir is not installed horizontally, water will flow at a higher ratio from its lowest point, while some other areas may have less water or even appear dry.

Considering construction limitations (i.e. level consistency in a very long weir) and/or selected materials (i.e. rough stone or joints between the slabs) the installed weir may not be uniformly leveled. Therefore, we recommend that the thickness of the water at the weir edge shall be designed at double the depth of any imperfections along the weir. This will ensure that your waterfall will appear to be flowing evenly from the entire weir length.

For example, if the designed water depth at the weir is set at 1/4" (6 mm) the weir installation shall be done within 1/8" (3mm) margin of perfection along its entire length. This required perfection of weirs installation may be also affected over time by uneven settlement of the structure. That is why some waterfalls with long weirs and a shallow water depth often flow unevenly.

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Water Rotations Calculator

Based on the volume of water in the pools and the required water flow, this calculator allows you to estimate the frequency of water rotations in the designed system. Knowing the number of rotations per hour or time for one complete rotation of water in the system allows you to select the most appropriate filtering system for your water feature.

Small debris that may fall into the pool can be filtered with a standard sand filter that is commonly used for swimming pools. Frequency of this type of filtering is related to the pool location and its surroundings. In most projects, filtering water from these particles at 3 to 5 hour frequency will keep water visually clean. A standard, swimming pool sand filters (depending on the model) are designed to work with water flows of 60 to 140 GPM  or 3.7 to 8.8 L/s. This calculator allows you to select the most suitable sand filter for your project.

Frequency of rotating water in the pool may affect your selection of sanitation system (i.e. chlorine) and its connection to the plumbing. However, if water in pools is frequently and well aerated via waterfalls or fountain jets, it will be less prone to algae related issues. Algae have difficulties surviving in water that is aerated more than 3 times per hour (every 20 minutes). This calculator will allow to find out how often your water is being aerated.

In water feature projects that requires high flow rate (i.e waterfall or fountain with big jets) it is quite common that mechanical system is designed with two-pump system. For example if the required flow for a waterfall is 800 GPM or 50.4 L/s, the fist pump will provide flow required for filtering the water (i.e. 70 GPM or 4.4 L/s) while the second pump will provide the remaining flow (730 GPM or 46 L/s) directly to the feature, bypassing the filters and sanitation.


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Pipe Sizing Calculator

When selecting pipes for a water circulation system one has to consider the pipe material (i.e. PVC, CPVC, cooper, cast iron, etc) and the pipe Ø - size. Selection of the material is mostly related to the pipe functions and location. Size of the pipe is related to the velocity of water running through it.

Water flowing faster than 5 ft/s or 1.5 m/s wears down the pipe material at a ratio that may over time damage the plumbing system. On the other hand, considering that there may be some small debris flowing in the water, the designed flow shall be fast enough (min 1 ft/s or 0.3 m/s) to move small debris away and prevent it from settling at the bottom of the pipe, potentially clogging the line over time.

This calculator estimates the velocity of water based on the required water flow and the selected one of the standard pipe size - Ø. Based on the calculated here velocity of water, one can select the most appropriate pipe size for each section of the circulation system.

Friction of water flowing against the inside of a pipe affects the total "pressure loss" of the system. This resistance to the flow increases with higher velocity and needs to be considered in calculating pump pressure requirements for your water feature. Therefore, installing plumbing systems with slightly bigger pipe size than it is necessary may extend life of the plumbing and potentially reduce power consumption of the pump.

Considering that many water features are installed on top of an underground parking slab, knowing the size of circulation pipes installed below the pool floor may affect the size of space between the slab and the pool floor.

Also, contrary to common believe it is the velocity (not the pressure) of water that affects the force of water stream (Force=Mass x Velocity.) Knowing the velocity allows one to calculate height of the fountain or a horizontal distance of water spewing from a gargoyle.

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Evaporation Loss Calculator

Water from any water feature will gradually evaporate. This water loss needs to be compensated on regular basis by adding new water to the system .

This calculator allows you to estimate the average Evaporation Loss based on the Pool Area and Evaporation Ratio. The evaporation loss is provided here in US Gallons and Cubic ft. per day or Liters and Cubic Meters per day.

Evaporation ratio varies all the time and depends on constantly changing factors such as: wind, sun exposure, water and air temperature, air humidity and movement of water. Therefore, this ratio is practically impossible to calculate with good accuracy, as it will slightly vary every few minutes throughout each day.  Therefore, evaporation ratio can be only roughly estimated as an average value and may slightly vary at different circumstances.

For this calculation we recommend using a number between the two evaporation ratio values provided below . These two values are based on observations and experience collected from various sources. Keep in mind that it may slightly vary in your project area.

- Hot summer, sunny days - 1/4" or 6 mm per day
- Overcast sky, low temperature day - 1/8" or 3 mm per day

Knowing this value allows you to estimate requirements for the daily make-up-water volume that shall be added to the water feature in order to maintain the designed water level in the pools. If you are loosing more water than the estimated value in this calculator, it means that you may have other water loss, such as water splashing to the outside the pool area or some leaks in the plumbing system or pool waterproofing.

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Overflow Calculator

In the event of a significant rainfall or any accidental overfilling of the pools (i.e. forgetting to turn off the infill valve), your water feature may start spilling its water over the pool edge. This potential, undesired water surplus in the pools needs to be automatically removed from the system before it can cause some flooding related damage.

This calculator allows you to estimate the minimum Overflow requirements based on the Pool Area , potential Rainfall Intensity and the Infill Flow used to fill the pool from your water supply. The calculated here value of the overflow requirement shall be than used for selecting the appropriate size of the overflow fittings and its connection to the drainage system.

Rainfall intensity varies in all geographic locations. Therefore, the value provided below is only an example of the maximum rainfall intensity at a given location. You shall find out from your local meteorological database and use here the estimated value of the Maximum Rainfall Intensity in your project location.

In Vancouver Canada, the average (5 min duration) significant rain events range is ± 45 mm/h (1.77 inch/h) with a max. observed in 1998 reaching 60 mm/h (2.3 inch/h)

Regarding the Infill Flow line, for a typical water feature we recommend installing  a 2" line with +/- 50 GPM flow or 50mm line with +/- 3 l/s flow. Having a bigger than typical garden hose 3/4" or 19mm line will significantly speedup the initial infill or any maintenance top-up process, thus reducing your future  maintenance labor cost.

Keep in mind that the overflow system needs to work even if there is a power failure; therefore, it shall rely on gravity flow (not pumping) from the overflow fitting to your drainage system.

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"Water-in-transit" Calculator

Majority of recirculating water features with a waterfall have an upper pool (or series of pools) and a collection pool that supplies water necessary for the desired waterfall flow (see waterfall calculator above).

When a waterfall pump (with a predetermined flow rate) is turned on, a portion of water from the collection pool gets temporarily relocated to the upper pool(s). This "Water-in-transit", gradually rises water level in the upper pool(s) starting the waterfall action with a small trickle. As the water level in the upper pool(s) slowly rises, the intensity of the waterfall also increases. When after few minutes the pumped-out flow from the collection pool matches the flow of the waterfall, which brings water back to the collection pool, water levels in all pools stabilize at a new, dynamic elevations. When the pump is turned off, water from the upper pool(s) keeps flowing to the collection pool until the water level in the upper pools reaches the weir elevation. At that point "Water-in-transit" stops flowing and the initial, static water level in all pools is reestablished.

This calculator allows you to estimate the Volume of Water-in-transit based on the Collection Pool Area, Upper Pools Area and the  predetermined Waterfall Thickness. Also, this calculator will tell you what is the anticipated drop of water level in the collection pool.

Knowing the volume of the "Water-in-transit" and the resulting drop of water level at the collection pool may be critical for the overall design of the water feature mechanical system.

In some water feature projects, where the calculated drop of water level in the collection pool exceeds 1" or 25 mm, you may encounter some undesired consequences, like unnecessary loss of water.  In projects where the upper pool is much bigger than the collection pool, it may turn out that the collection pool is too small to feed the designed waterfall requirements. In some extreme circumstances, you may end up with an empty collection pool, which could result in malfunctions of mechanical system and/or its potential damage.

If the upper pool area more than doubles the size of the collection pool, you may have to consider adding to your system a "surge tank" that will collect and supply "Water-in-transit" necessary for the desired flow of the waterfall.

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