Graduated Pipette: Types, Uses, and How to Read It Accurately

A graduated (Mohr or serological) pipette has a scale of graduation marks that lets you deliver any volume within its range — unlike a volumetric pipette which delivers only one fixed volume. The trade-off is accuracy: a graduated pipette has wider tolerances than a volumetric pipette at the same volume. Use it when flexibility matters more than the tightest possible tolerance.

Pick by the job, not by habit

  • Variable volume 1–25 mL, flexibility needed
    Graduated (Mohr or serological) pipette
    Multi-mark scale; deliver any volume within range
  • One precise fixed volume, tightest tolerance
    Volumetric (one-mark) pipette
    Single calibration mark = tightest available tolerance at that volume
  • Sub-mL volumes (µL range)
    Micropipette
    Graduated pipettes start at 0.1–0.5 mL; micropipettes cover µL accurately
  • Blowing out the tip is required (TC application)
    Serological pipette
    Graduations to the tip; calibrated to be blown out completely
  • Not blowing out (TD application)
    Mohr pipette
    Graduations stop before tip; deliver between marks, do not blow out
  • Cell culture media, reagent transfers
    Serological pipette with pipette aid
    Standard for sterile large-volume transfers in cell biology

Burette vs pipette, side by side

  • Graduations
    Stop before the tip
    Continue to the tip
  • Calibration type
    TD (To Deliver) — do not blow out
    TC (To Contain) — blow out completely
  • ISO tolerance (10 mL)
    ±0.10 mL (Class B)
    ±0.05–0.10 mL depending on class
  • Typical use
    General chemistry, titration prep
    Cell culture, media, sterile transfers
  • Sterile available
    Less common
    Standard; individually wrapped
  • Pipette aid needed
    Optional (mouth pipetting historic)
    Required; never mouth-pipette

Mohr vs serological — the graduation difference that matters

Both are graduated pipettes, but they differ at the tip. A Mohr pipette has graduations that stop before the tip — the ungraduated section at the bottom means you always deliver between two marks, never to the tip. A serological pipette has graduations all the way to the tip, and is designed to be blown out completely (TC — To Contain). Blowing out a Mohr pipette over-delivers; not blowing out a serological under-delivers. Check the marking before use.

How to read a graduated pipette accurately

Graduated pipettes are read top-down: the zero mark is at the top, and volume increases toward the tip. Deliver from one graduation mark to another — do not try to interpolate to partial marks for critical work. Read the bottom of the meniscus with the eye exactly level. Parallax error (reading from above or below) on a graduated pipette is more consequential than on a volumetric because you are interpolating between marks rather than reading a single calibration point.

Three accuracy limits of graduated pipettes

  1. Tolerance is wider than volumetric. ISO 835 tolerances for a 10 mL graduated pipette are ±0.05–0.10 mL depending on class — two to four times wider than a one-mark volumetric at the same volume.
  2. Partial-mark interpolation adds error. Reading between graduation marks introduces operator-dependent error. For critical volumes, use a volumetric pipette or a micropipette.
  3. TD vs TC confusion. Mohr pipettes are TD (do not blow out); serological are TC (blow out). Mixing up the two introduces a systematic volume error equal to the tip residual.

Standards

  • ISO 835:2007
    Graduated pipettes — capacity, graduation intervals, and tolerance classes
  • ISO 648:2008
    One-mark volumetric pipettes — for comparison of tolerance at same volume
  • ISO 4787:2021
    Laboratory glassware — volumetric instruments; methods for testing and use

Frequently asked questions

  • What is a graduated pipette used for?
    Delivering variable volumes within its range — from 0.1 mL to 25 mL depending on size. Used when flexibility matters more than the tightest tolerance, such as media transfers and reagent additions.
  • What is the difference between a Mohr and a serological pipette?
    A Mohr pipette has graduations that stop before the tip (TD — do not blow out). A serological pipette has graduations to the tip (TC — blow out completely). Confusing the two introduces systematic volume error.
  • Is a graduated pipette less accurate than a volumetric pipette?
    Yes, at any given volume. A graduated pipette's tolerance (ISO 835) is typically two to four times wider than a volumetric pipette (ISO 648) at the same volume. Use volumetric when the tightest tolerance is required.
  • How do I read a graduated pipette correctly?
    Read top-down (zero at top), deliver between graduation marks, and read the bottom of the meniscus with your eye level with the liquid surface. Avoid interpolating between marks for critical work.
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