<em>Accuracy</em> is how close a value is to the truth; <em>precision</em> is how fine or how repeatable it is. A scale that reads 70.0 kg for a genuine 70 kg load is accurate; one that reads 68.31, 68.29 and 68.30 for that same load is precise but inaccurate. The two are independent — a number can be wrong to five decimal places.
The core difference
In everyday speech these words are treated as synonyms, and in most sentences nobody minds. In science, engineering, statistics, manufacturing and data work they mean two different things, and confusing them causes real errors.
Accuracy answers: how close is this to the actual value? Precision answers two related questions — how finely is it expressed, and how consistently does it come out on repeat measurement?
The dartboard picture
- All three darts in the bullseye: accurate and precise.
- All three darts tightly grouped in the top-left corner: precise but not accurate — there is a systematic bias.
- Three darts scattered around the bullseye: accurate on average but not precise.
- Three darts scattered across the wall: neither.
The second case is the dangerous one, because tight grouping looks like quality. A miscalibrated instrument is confidently, repeatably wrong.
How to use each
Accuracy: "Check the accuracy of the figures against the source data." "The forecast proved accurate to within two per cent."
Precision: "The lathe works to a precision of 0.01 mm." "Reporting the population as 3,472,918 implies a precision the census cannot support."
The test
Ask which question you are answering. "Is it right?" is accuracy. "How finely, or how consistently?" is precision. A quicker version: if you could rephrase using "correct", you mean accuracy; if you could rephrase using "to how many decimal places" or "how repeatable", you mean precision.
Being honest about ordinary usage
Outside technical contexts, this distinction is not observed and there is no need to enforce it. "He described the scene with great precision" simply means in fine detail, and nobody reads it as a claim about repeatability. Dictionaries record precise as a synonym of exact and accurate, and that use is entirely standard English.
Where it matters is any writing that touches measurement, data or instruments. There, spurious precision is a genuine failure: quoting a converted figure as 6.2137 miles when the original said "about 10 km" adds digits without adding truth. The rule for such writing is to report only as many digits as your measurement justifies, and to state accuracy separately — typically as a tolerance or margin of error.
Frequently Asked Questions
Can something be precise but not accurate?
Yes, and it is the most common failure in measurement. An instrument with a calibration offset gives tightly clustered readings that are all wrong by the same amount — high precision, low accuracy.
Is "more precise" the same as "more exact"?
In everyday English, effectively yes. In technical writing, no: more precise means more finely resolved or more repeatable, which is not a claim that the value is closer to the truth.
Which matters more in data reporting?
Accuracy, usually — a wrong number helps nobody. But false precision is its own error, because extra decimal places signal a confidence the underlying data does not support. Report to the precision your method actually achieves.