Useful conversions
Pump specifications mix litres, cubic metres, gallons, bar, metres and inches. Use the converter or the tables below to compare pumps, hoses and fittings on the same basis. All gallons on this page are UK (imperial) gallons unless marked US.
Quick converter
100 l/min = 6.00 m³/h
Conversion factor: 1 l/min = 0.0600 m³/h
Water head figures assume clean water at around 4 to 20°C.
Flow rate conversions
Pump flow is usually quoted in litres per minute (l/min) or cubic metres per hour (m³/h). 1 m³/h is about 16.7 l/min.
| To convert | Into | Multiply by |
|---|---|---|
| l/min | m³/h | 0.06 |
| m³/h | l/min | 16.67 |
| l/s | l/min | 60 |
| l/min | l/s | 0.0167 |
| l/s | m³/h | 3.6 |
| m³/h | l/s | 0.278 |
| l/min | UK gal/min | 0.220 |
| UK gal/min | l/min | 4.546 |
| l/min | UK gal/h | 13.20 |
| l/min | US gal/min | 0.264 |
| US gal/min | l/min | 3.785 |
| l/min | l/s | m³/h | UK gal/min |
|---|---|---|---|
| 50 | 0.83 | 3.0 | 11.0 |
| 100 | 1.67 | 6.0 | 22.0 |
| 150 | 2.50 | 9.0 | 33.0 |
| 200 | 3.33 | 12.0 | 44.0 |
| 300 | 5.00 | 18.0 | 66.0 |
| 500 | 8.33 | 30.0 | 110.0 |
| 1,000 | 16.67 | 60.0 | 220.0 |
| 2,000 | 33.33 | 120.0 | 439.9 |
Pressure and head conversions
Pumps are rated by "head", the height in metres a pump can lift water. Pressure gauges read in bar or psi. As a rule of thumb, 1 bar is about 10 metres of head, and 10 metres of head is about 1 bar or 14.5 psi.
Maximum head is the height at which flow drops to zero, so a pump always delivers less water the higher it has to lift. Long hose runs and small hose sizes add friction, which works like extra height. Use our Pump Performance Calculator to allow for both.
| To convert | Into | Multiply by |
|---|---|---|
| bar | metres of water | 10.2 |
| metres of water | bar | 0.098 |
| bar | psi | 14.5 |
| psi | bar | 0.069 |
| psi | metres of water | 0.703 |
| metres of water | psi | 1.42 |
| metres of water | feet of water | 3.281 |
| feet of water | psi | 0.433 |
| bar | kPa | 100 |
| bar | metres of head | psi | feet of head |
|---|---|---|---|
| 0.5 | 5.1 | 7.3 | 16.7 |
| 1 | 10.2 | 14.5 | 33.5 |
| 1.5 | 15.3 | 21.8 | 50.2 |
| 2 | 20.4 | 29.0 | 66.9 |
| 3 | 30.6 | 43.5 | 100.4 |
| 4 | 40.8 | 58.0 | 133.8 |
| 5 | 51.0 | 72.5 | 167.3 |
| 6 | 61.2 | 87.0 | 200.7 |
BSP sizes in mm
Fittings are sized by their nominal BSP (British Standard Pipe) size in inches, but hose is sized by its bore in millimetres. That is why the same fitting can be called 1 inch or 25mm. The thread itself is wider than the nominal size: a 1 inch BSP male thread measures about 33mm across, not 25mm. On our site, sizes are shown in mm with the matching BSP size.
| BSP size | Our size label | Typical hose bore | Male thread outside diameter |
|---|---|---|---|
| ½" | 12mm | 13mm | 20.96mm |
| ¾" | 18mm | 20mm | 26.44mm |
| 1" | 25mm | 25mm | 33.25mm |
| 1¼" | 32mm | 32mm | 41.91mm |
| 1½" | 38mm | 38 or 40mm | 47.80mm |
| 2" | 50mm | 50mm | 59.61mm |
| 2½" | 62mm | 63 or 65mm | 75.18mm |
| 3" | 75mm | 75 or 80mm | 87.88mm |
| 4" | 100mm | 100mm | 113.03mm |
| 6" | 150mm | 150mm | 163.83mm |
Measuring an unknown thread
Measure across the outside of a male thread (or the inside of a female thread) with a ruler or calipers and match it to the right-hand column. Then choose the BSP size in that row.
Volume conversions
| To convert | Into | Multiply by |
|---|---|---|
| m³ | litres | 1,000 |
| litres | m³ | 0.001 |
| m³ | UK gallons | 220 |
| UK gallons | litres | 4.546 |
| litres | UK gallons | 0.220 |
| US gallons | litres | 3.785 |
| UK gallons | US gallons | 1.201 |
Working out the water in a flooded space: length (m) × width (m) × depth (m) = cubic metres. Multiply by 1,000 for litres.
Weight and length
| Weight | Equals |
|---|---|
| 1 kg | 2.205 lb |
| 1 lb | 0.454 kg |
| 1 litre of water | about 1 kg |
| 1 m³ of water | about 1,000 kg (1 tonne) |
| Length | Equals |
|---|---|
| 1 inch | 25.4 mm |
| 1 mm | 0.0394 inches |
| 1 metre | 3.281 feet |
| 1 foot | 0.305 metres |
| 1 km | 0.621 miles |
Worked examples
-
How long to empty a flooded cellar?
A cellar 5m × 4m with 1m of water holds 5 × 4 × 1 = 20 m³, or 20,000 litres. A pump delivering 200 l/min at the height and hose length you need will take 20,000 ÷ 200 = 100 minutes, about 1 hour 40 minutes. Check the flow at your actual head, not the maximum flow.
-
What pressure will a 30m head pump give?
30 metres of head ÷ 10.2 is about 2.9 bar, or roughly 43 psi, at zero flow. In use the pressure will be lower.
-
Pond turnover
A 10,000 litre pond turned over every 2 hours needs 10,000 ÷ 120 = about 83 l/min, or 5 m³/h, at the height of your filter or waterfall.
-
Comparing a spec in gallons
A pump quoted at 50 UK gallons per minute moves 50 × 4.546 = about 227 l/min, or 13.6 m³/h. If the figure is US gallons it is 50 × 3.785 = about 189 l/min.
-
Which fitting fits a 25mm hose?
A 25mm bore hose takes a 1 inch BSP hose tail. The threaded end of that fitting will measure about 33mm across.
Frequently asked questions
How many litres per minute is 1 m³/h?
1 cubic metre per hour is about 16.7 litres per minute. To convert l/min to m³/h, multiply by 0.06.
How many metres of head is 1 bar?
1 bar is about 10.2 metres of water head. For quick estimates, 1 bar is roughly 10 metres.
How do I convert psi to bar?
Multiply psi by 0.069. For example, 30 psi is about 2.1 bar.
What is 1 inch BSP in mm?
A 1 inch BSP fitting suits 25mm bore hose and pipe, but the male thread itself measures about 33.25mm across the outside.
Are the gallons on pump specifications UK or US gallons?
UK and European specifications normally use UK (imperial) gallons of 4.546 litres. US specifications use US gallons of 3.785 litres, so a US gallon figure is about 17% smaller.
How do I work out how long a pump will take to empty a space?
Multiply length × width × depth in metres to get cubic metres, multiply by 1,000 for litres, then divide by the pump's flow in l/min at your actual head. The answer is in minutes.
Does hose length affect how much a pump delivers?
Yes. Friction in the hose acts like extra height, so long runs or narrow hose reduce flow. Our Pump Performance Calculator allows for hose length and size.
