The ideal breast pump suction level is the highest setting that still feels comfortable, not the maximum your pump can reach. Most pumps operate between 50 and 250 mmHg of vacuum pressure, but the sweet spot for milk output sits around 150 mmHg for most people. Going higher than that doesn’t produce more milk and can cause nipple damage.
What the Numbers Actually Mean
Breast pump suction is measured in millimeters of mercury (mmHg), the same unit used for blood pressure. Consumer and hospital-grade pumps typically range from about 50 mmHg on the lowest setting to 250 mmHg at maximum. A hospital-grade pump like the Medela Symphony spans that full 50 to 250 mmHg range, while personal pumps like the Medela Pump in Style range from about 100 to 250 mmHg in their expression phase.
For context, a vaginally born newborn naturally sucks at roughly 150 mmHg. A baby born via cesarean tends to suck closer to 100 mmHg. These numbers from infant feeding research provide a useful reference point: the pressure a healthy newborn generates is essentially what your body was designed to respond to.
Why Higher Suction Doesn’t Mean More Milk
A randomized controlled study published in Maternal & Child Nutrition compared pumping at 150 mmHg versus 100 mmHg in mothers after cesarean delivery. The higher-pressure group produced an average of 158 grams of milk per day compared to 103 grams in the lower-pressure group, a significant difference. But the researchers deliberately chose not to test pressures above 150 mmHg, because prior research had already shown that exceeding normal infant suction strength provides no additional benefit.
In fact, excessively high suction (averaging around 233 mmHg in one cited study) was associated with severe pain and nipple injuries. The relationship between suction and output is not linear. There’s a ceiling, and pushing past it works against you by causing tissue damage that can make future pumping sessions painful and less productive.
How to Find Your Comfort Level
The practical method is straightforward: start at the lowest suction setting and gradually increase it until you feel a strong pull that is not painful. This is sometimes called your “maximum comfort vacuum.” If you feel any pinching, stinging, or sharp discomfort, turn it back down. The level just below the point of discomfort is where you want to stay.
Your comfort level will shift over time and even between sessions. Engorgement, time of day, stress, and how recently your baby nursed all affect how your breasts respond to vacuum pressure. It’s worth rechecking your setting each session rather than locking in one number and forgetting about it. Some days you’ll tolerate a higher level, and some days you’ll need to dial back.
Stimulation Mode vs. Expression Mode
Most modern pumps have two distinct phases. The stimulation (or massage) phase uses low suction with rapid cycles to mimic the quick, fluttery sucking pattern a baby uses to trigger your let-down reflex. Once milk starts flowing, the pump switches to expression mode, which uses stronger suction at a slower rhythm, mimicking the deep, steady suck of a feeding baby.
You generally don’t need to adjust the stimulation phase much. It’s designed to be light and fast. The setting that matters most is your expression mode suction level, since that’s the phase doing the actual milk removal. Some pumps like the Spectra SG let you control suction strength and cycle speed independently, with up to 12 expression levels. Others are simpler, offering a single dial. Either way, the same principle applies: increase until it’s strong but comfortable, then stop.
Flange Fit Changes Everything
Your suction setting only works properly if your flange (the funnel-shaped piece that sits over your nipple) fits correctly. A poorly fitting flange changes how the vacuum reaches your breast tissue, which can make any suction level feel either too weak or painfully strong.
A pilot study comparing flange sizing methods found that participants using a smaller, more precisely fitted flange pumped an average of 15 grams more milk per session and reported significantly better comfort compared to the traditional sizing approach. The newer thinking is that the best fit starts with a flange size very close to your actual nipple tip diameter, rather than the older recommendation of adding several millimeters of room. If you’re struggling with comfort at any suction level, an incorrect flange size is one of the most common culprits.
Signs Your Suction Is Too High
Your body gives clear signals when the vacuum pressure is excessive:
- Pain during pumping. A strong pulling sensation is normal. Sharp, burning, or stinging pain is not.
- Nipple blanching. If your nipple turns white during or after pumping, blood flow is being restricted by too much pressure.
- Cracked or fissured nipples. Repeated sessions at excessive suction can cause visible cracks in the nipple skin, sometimes with bleeding.
- Swelling or warmth. If your nipple looks puffy or feels warm to the touch after pumping, you’ve likely been using too much suction or pumping for too long.
Any of these signs means you should reduce your suction level immediately. Continuing to pump through pain doesn’t build supply. It creates inflammation that can actually reduce output and make you dread the pump, which further suppresses let-down.
A Practical Starting Point
If your pump displays numbered levels rather than mmHg values, aim for the middle range of available settings as your starting point, then adjust up or down from there. If your pump does show mmHg, somewhere around 150 mmHg during expression mode is a reasonable target for most people, based on the vacuum pressure a healthy newborn generates. But your own comfort is the final authority. A setting of 120 mmHg that feels right will almost always outperform a setting of 200 mmHg that makes you tense up.
If you live at a high elevation (above 3,300 feet), your pump’s effective maximum suction drops. At elevations above 6,600 feet, maximum output may be closer to 200 mmHg rather than 250 mmHg. This is a physics issue, not a pump malfunction, and it doesn’t usually affect your ability to pump effectively since optimal suction is well below most pumps’ maximum anyway.