• How To Calculate The Flowrate Of A Pump

Shopping Basket

Welcome to Water Gardening Direct, your "One-Stop solution" for all your
Pond Equipment, Water Features and Spare Parts.
We hope our site has all the Help and Advice you need, but if not
please feel free to give us a call on 01778 341199
or click here to order or download our FREE Brochure

How To Calculate The Flowrate Of A Pump

You Are Here : Help and Advice > Pond Advice > How To Calculate The Flowrate Of A Pump

How To Calculate The Flowrate Of A Pump - Pump Flowrate Calculator

Have you ever had a situation where you suspect that a pump may have slowed down, or may need to be upgraded / improved. Well here is an easy way to check.

  1. First, get a container that can be used to collect the water from the Pump / Waterfall (ideally, this should be at least 2 gallons or 9 litres, as accuracy is increased with a bigger container.
  2. Secondly you will need a watch with a second hand to measure the time in seconds.
  3. Now the best bit. Time how long it takes in seconds to fill the container up, with the water coming out of the Pump / Filter or from the waterfall and then answer the following question and press calculate.

What Unit of measurements would you like to use:
Metres & Litres  or   Feet & Gallons


How long did it take (in Seconds): 


Why Might The Flowrate Be Low ?

The main thing to remember, is that there are a lot of causes for lower than expected flowrates, other than a faulty pump. In fact, the most common cause of a low flowrate is the way in which it has been installed. Before you come to the conclusion that a pump is under performing, have a look at some possible causes.

Start off with the easy stuff, is the pump clogged up, has one of the flexible pipes been blocked or squashed. Checking the basics is always the best way to start. And don't forget, if you are using a filter with a spray bar, remember to check that it is not blocked up with blanket weed.


  • Head Lift :-
    This is an expression which describes the vertical distance between the surface of the pond and the top point that you are pumping to. When checking the expected performance of your pump, you will see from the manufacturers details, that the higher you pump the water, the slower the flowrate will be. Remember that if your system contains a filter and UV, you should allow about 2ft (0.6m) additional lift, for the "back pressure" that these units produce
  • Pipe Size :-
    When the manufacturer of your pump states any particular flowrates, remember that this will be when the pump is using the biggest possible pipe size. If you have used a smaller size, you will experience substantial reductions in the flowrate
  • Connectors:-
    Many manufacturers supply products with variable sized connectors, which have to be cut back to suit your pipework. Double check all connectors to ensure that they have been fully cut back, to allow as much water through as possible.
  • Frictional Resistance:-
    This is a slightly more complex issue. Frictional Resistance refers to the energy (flowrate) lost due to the rubbing effect of the water against the side of the pipework. To minimise this loss, keep your pipework as short, straight and simple as possible.

Customers Reviews


Why Buy From Us

FREE Delivery for Orders Over £50
(Uk mainland excluding Highlands of Scotland and Islands)
1000's of Happy CustomersTick
1000's of Products in StockTick
Free Help and Advice from our Experienced Technical StaffTick
Over 10 Years Mail Order ExperienceTick

Secure Payments

Secure Online Payments

Follow Us