The exact factor: add three zeros
Milli is one thousandth of a litre, micro is one millionth. They sit a factor of 1000 apart, so converting is just moving the decimal three places: mL to uL, multiply by 1000 (add three zeros); uL to mL, divide by 1000. The factor is exact, so there is no rounding in the conversion itself.
Common pipetting volumes
| Millilitres | Microlitres | Typical use |
|---|---|---|
| 0.001 mL | 1 uL | Enzyme or primer aliquot |
| 0.01 mL | 10 uL | HPLC injection, P10 range |
| 0.02 mL | 20 uL | P20 pipette |
| 0.025 mL | 25 uL | PCR reaction mix |
| 0.2 mL | 200 uL | P200 pipette, PCR tube |
| 0.5 mL | 500 uL | Swab sample |
| 1 mL | 1000 uL | P1000, full pipette range |
Air-displacement pipettes cover 0.5 to 1000 uL across the P10, P20, P200 and P1000 ranges, which is why lab protocols are written in microlitres even when the bulk volume is stated in mL.
A slipped decimal is a 1000x error
- uL and mL differ by a thousand. Reading uL as mL, or vice versa, is off by 1000x. Pipetting 1 uL where 1 mL was meant ruins the run, so check the symbol twice.
- Round at the end, not partway. 0.333 mL is 333 uL; rounding the mL to 0.33 first drops it to 330 uL and the error compounds through later steps.
- The factor is exact; your pipette is not. The math is precise, but a P20 carries a tolerance of roughly plus or minus 2 percent, so a nominal 20 uL is really about 19.6 to 20.4 uL. Calibrate for critical work.
Common questions
How many microlitres are in a millilitre?
Exactly 1000. One millilitre is 1000 microlitres, because milli means one thousandth and micro means one millionth, a factor of a thousand apart. The relationship is exact, not rounded.
How do I convert mL to uL quickly?
Multiply by 1000, which is the same as adding three zeros. So 2.5 mL is 2500 uL, and 0.05 mL is 50 uL. To go the other way, divide by 1000, or move the decimal three places left.
Is 0.5 mL the same as 500 uL?
Yes. 0.5 x 1000 = 500, so 0.5 mL and 500 uL are exactly equal. Pipettes are usually labelled in uL, so a protocol asking for 0.5 mL means setting a P1000 to 500.
