Pumping speed is the volume of gas a vacuum pump removes per unit of time — quoted in m3/h for rough and medium-vacuum pumps, or litres per second (l/s) for high-vacuum pumps. It determines how quickly you can pump down a chamber. It is not the same as ultimate vacuum, which is the deepest pressure the pump can reach.
Pumping speed vs ultimate vacuum
These are the two headline specs of any pump, and they answer different questions. Pumping speed tells you how fast; ultimate vacuum tells you how deep. For example, the two-stage Edwards E2S pumps at 5–12 m3/h to an ultimate of 2×10-3 mbar, while a Leybold TURBOVAC i turbo runs at 90–1390 l/s to reach ultra-high vacuum. You need both figures to size a pump.
Displacement vs effective speed
Datasheets often quote displacement (the swept volume, a theoretical maximum) and effective pumping speed (what you actually get at the inlet). Effective speed is the one that matters, and it’s always a little lower than displacement.
Speed changes with pressure
A pump’s speed is not constant — it falls as the pressure drops towards the ultimate vacuum, which is why manufacturers publish a pumping speed curve. When sizing, look at the speed at your working pressure, not just the headline figure.
How to use pumping speed to size a pump
Bigger chambers and faster pump-down times need more speed; heavy gas or vapour loads need more again, or a Roots booster. Too little speed and the process drags; too much wastes money and energy. If in doubt, tell us your chamber volume and target time and we’ll size it.
Not sure what pumping speed you need?
Give us your chamber size, target pressure and pump-down time and we’ll specify the right pump. Email [email protected] or request a quote.
Frequently asked questions
What is the difference between pumping speed and ultimate vacuum?
Pumping speed is how fast a pump removes gas (m3/h or l/s); ultimate vacuum is the deepest pressure it can reach (mbar). One measures speed, the other measures depth – you need both to choose a pump.
What units is pumping speed measured in?
Rough and medium-vacuum pumps are quoted in cubic metres per hour (m3/h); high-vacuum pumps such as turbomolecular pumps are quoted in litres per second (l/s).
How do I choose the right pumping speed?
Match it to your chamber volume, required pump-down time and gas or vapour load, and check the pump’s speed at your working pressure – not just the headline figure, because speed falls as pressure drops.
Written by the Girovac technical team. Girovac Ltd has supplied and serviced industrial and laboratory vacuum equipment from its North Walsham workshop since 1983. Last updated: July 2026.