How this instrument works
The litre is not an SI base unit at all; SI treats it as one permitted nickname for the cubic decimetre. One cubic decimetre holds 1000 cubic centimetres, and the prefix milli- cuts that litre into one thousand parts, so millilitres and cubic centimetres describe identical volume by pure arithmetic. Writing cc instead of cm³ is workshop habit, kept alive by typewriters and parts catalogues with no superscript key.
That equality has not always held. In 1901 the 3rd CGPM redefined the litre as the volume occupied by one kilogram of pure water at its temperature of maximum density under standard atmospheric pressure — wording tied to matter rather than to geometry. Careful measurement later put that volume at 1.000028 dm³, so for sixty-three years one millilitre ran about 28 parts per million larger than one cubic centimetre. Analysts reporting five significant figures had to say which of the two they meant, and glassware was graduated accordingly.
The 12th CGPM ended that split in 1964, withdrawing the water wording and returning the litre to exactly one cubic decimetre. Since then this factor has been 1.0 with no uncertainty attached to it. Where the two units still diverge is habit: displacement is quoted in cc across motorcycling and small-engine work, which is why race classes carry names like 125, 250 and 650, while pharmacy and nursing dispense in ml, and style guidance in print asks for cm³ or ml and nothing else.
- Type the volume you have into the Millilitres (ml) field; 250 is loaded to start.
- Read the Cubic centimetres (cc) line beneath it, which recomputes as you type.
- Going the other way needs no second tool: any reading in cc is already the same number of ml, so enter it and confirm.
- For litres, shift the decimal three places — 1500 ml is 1.5 L and 1500 cc.
Worked example — 250 ml on the burette
An engine builder cc'ing the cylinder head of a 250 trail bike fills the chamber from his burette, graduated in millilitres, and stops the meniscus at 250 ml. Entering 250 into the Millilitres (ml) field returns 250.0 on the Cubic centimetres (cc) line — the same figure cast into the crankcase, because that badge was never another measurement, only another spelling.
That check is worth making precisely because nothing moves: if spec sheet, syringe barrel and burette disagree about 250, the disagreement lives in glassware, fluid temperature or the meniscus you read, never in the conversion itself. Water warming inside cold glass swells by roughly 0.02 percent per degree near room temperature, which outweighs anything this factor could introduce.
Questions
Is one millilitre exactly one cubic centimetre?
Yes, exactly rather than approximately. The litre is defined as one cubic decimetre, which contains 1000 cubic centimetres, and milli- means one thousandth of that litre. This chain is decimal arithmetic with no measured quantity anywhere in it, so the factor is 1.0 with zero uncertainty and nothing to round. Any gap you observe between two readings of the same liquid comes from the glassware or its temperature.
Were millilitres ever different from cubic centimetres?
Yes, between 1901 and 1964. The 3rd CGPM tied the litre to the volume of one kilogram of water at maximum density, which later measurement put at 1.000028 cubic decimetres rather than exactly one. Millilitres of that era therefore ran about 28 parts per million larger than cubic centimetres — irrelevant for dosing, visible in careful analytical work, and the reason older papers name their unit so deliberately. The 12th CGPM removed the water wording in 1964, and the two have been identical since.
Why are engines measured in cc and medicines in ml?
Trade habit, hardened over roughly one century. Displacement is geometry — bore, stroke and cylinder count multiplied out — so engineers reached for cubic centimetres, and racing classes ended up named after them: 125, 250, 650. Fluids are poured and graduated, so pharmacy stayed inside the litre family. Above roughly one litre the motor industry switches too, which is how 1998 cc reaches the showroom badged as 2.0.
Should I write cc, cm³ or ml?
Write ml for dosing and cm³ where cubic form matters; cc is not an SI symbol, and standards documents leave it out. In clinical records this preference goes beyond style — the Institute for Safe Medication Practices puts cc on its error-prone abbreviation list, because hurried handwriting turns cc into what looks like two zeros, or into the u for units, so 5 cc can be dispensed as something far worse. Machine shops and parts catalogues can keep cc; prescriptions should not.
How many cc are in one cubic inch?
Exactly 16.387064 cc. The inch has been exactly 25.4 mm since the 1959 international yard and pound agreement, and 25.4³ works out to 16387.064 cubic millimetres. That factor sits behind the old displacement arithmetic: the 350 cubic inch V8 sweeps 5735.5 cc, near enough to the 5.7 litres on the badge. Since cc and ml are the same size, that answer is also 5735.5 ml.
Does the liquid change the answer?
No — this is volume-to-volume conversion, so 250 ml of mercury, olive oil or air is 250 cc of each. What the substance changes is mass: 250 ml of water weighs close to 250 g, while the same volume of mercury comes to about 3.4 kg. Mixing up the two is the most common real error here, particularly when labels state strength as mg per ml. The volume converts freely; the dose behind it does not.