To set a micropipette volume, you turn the adjustment dial on the plunger: clockwise to increase the volume, counterclockwise to decrease it. The three-digit display on the pipette shows your selected volume, but the way you read those digits depends on which pipette size you’re using. Getting this right matters because even a small misread can throw off your results by tens or hundreds of microliters.
How the Adjustment Dial Works
Most manual micropipettes have a rotating dial (sometimes called the plunger knob or thumbwheel) at the top of the instrument. Turning it moves a set of numbered rings visible through a small window on the pipette body. Some pipettes use a single knob, while others have stacked rings you turn independently for coarse and fine adjustments.
Turn clockwise to increase volume and counterclockwise to decrease it. This is the standard convention across major manufacturers like Eppendorf, Gilson, and Rainin, though you should confirm with your specific model since a few pipettes reverse this. The dial typically has a smooth mechanical feel with light resistance, and you’ll see the numbers in the display window scroll as you turn.
Reading the Volume Display
The three-digit display is where most beginners trip up, because the same reading of “100” means something completely different depending on which pipette you’re holding. Each pipette size assigns different units to each digit position.
P1000 (100–1000 µL)
The top digit (often printed in red) represents thousands of microliters. The middle digit is hundreds, and the bottom digit is tens. A display reading “100” from top to bottom means 1,000 µL. A reading of “065” means 650 µL. Small tick marks below the bottom digit represent single microliters.
P200 (20–200 µL)
The top digit is hundreds, the middle is tens, and the bottom is ones. A display reading “100” means 100 µL. A reading of “095” means 95 µL. The tick marks at the bottom represent tenths of a microliter.
P20 (2–20 µL)
The top digit is tens, the middle is ones, and the bottom digit (often in red) is tenths. A display reading “100” means 10.0 µL. A reading of “022” means 2.2 µL. The tick marks here represent hundredths of a microliter, giving you extremely fine resolution for small volumes.
The red-colored digit is your best visual cue. On a P1000, the red digit is at the top (thousands). On a P20, it’s at the bottom (tenths). If you’re ever unsure which pipette you’re holding, the red digit tells you the scale.
The Dial-Down Technique
There’s a specific habit that separates careful pipetters from sloppy ones: always approach your target volume by dialing down, not up. This isn’t just a preference. The gears inside the adjustment mechanism have tiny amounts of play, called mechanical backlash, that can leave you slightly off your intended volume if you stop while dialing upward.
If your target volume is lower than the current setting, simply dial down to it. If your target is higher, dial about a third of a turn past the number you want, then dial back down to it. This ensures the internal piston settles at the correct position. It takes an extra second and eliminates a common source of inaccuracy that’s invisible on the display.
Staying Within the Volume Range
Every micropipette has a minimum and maximum volume printed on the body. Never set the dial above the maximum or below the minimum, even if the dial physically allows you to keep turning. Going past these limits can damage the internal piston seal, and any volume you aspirate outside the rated range will be inaccurate.
A good rule of thumb: use a pipette in the upper half of its range whenever possible. A P200 set to 25 µL will be less precise than a P20 set to the same volume. If you need 150 µL, grab the P200 rather than trying to do two pulls with a P20. ISO 8655, the international standard for pipette accuracy, tests pipettes at 10%, 50%, and 100% of their nominal volume, and the permitted error is proportionally larger at the low end. For example, a P10 is allowed an error of ±0.120 µL at 1.0 µL, which is a 12% deviation, while the same absolute error at 10.0 µL would only be 1.2%.
Using the Volume Lock
Many pipettes have a locking mechanism, usually a small lever, button, or twist ring near the dial, that prevents the volume from shifting during use. Once you’ve set your desired volume, engage the lock before you start pipetting. This is especially useful during repetitive work where your thumb is constantly pressing the plunger, since the friction and handling can nudge the dial slightly without you noticing. If your pipette has a lock and you’re not using it, you’re introducing unnecessary risk into every experiment.
Avoiding Parallax Errors
On older pipettes or models with a mechanical display window, the angle you look at the numbers matters. If you read the display from above or below instead of straight on, you can misread which tick mark the indicator line is pointing to. This is the same parallax effect that makes a car speedometer look different from the passenger seat.
Hold the pipette upright at eye level and look straight at the display window. The indicator line should appear centered between the front and back edges of the number ring. This is less of an issue on newer pipettes with flat digital-style number wheels, but it’s worth building the habit regardless of your equipment.
Setting Volume on Electronic Pipettes
Electronic micropipettes replace the manual dial with a digital screen and buttons or a scroll wheel. You select your volume on the display, often in increments as fine as 0.1 µL, and the motorized piston moves to the exact position. The advantage is that there’s no mechanical backlash, no parallax to worry about, and the display is unambiguous.
Most electronic models also let you store preset volumes and switch between them with a button press, which saves time during protocols that require multiple volume changes. The tradeoff is cost, battery dependence, and slightly more weight in your hand during long pipetting sessions. The volume-setting principle is the same, though: select a number within the pipette’s rated range, confirm it on the display, and begin aspirating.
Quick Reference for Common Settings
- 1 µL: P2 or P10, display reads near the low end of the range
- 10 µL: P20 (display reads “100”), or P10 at maximum
- 50 µL: P200 (display reads “050”)
- 100 µL: P200 (display reads “100”)
- 500 µL: P1000 (display reads “050”)
- 1000 µL: P1000 (display reads “100”)
Notice that “100” on the display means maximum volume for every pipette size. If you see “100” and aren’t sure which pipette you’re holding, check the label on the body. Setting a P200 to what you think is 100 µL when you’re actually holding a P1000 would give you 1,000 µL, a tenfold error.