CEP1 (circular error probable)

CEP stands for circular error probable. It is a statistical measure of accuracy. In a circular normal distribution, the CEP is the radius of the circle that contains 50% of the individual measurements, or the radius within which there is a 50% probability that the measured point will fall. The standard abbreviation is CEP, and this page covers the measure that "CEP1" refers to. See the dual-use control wording for guidance sets for the formal text.

For missiles and munitions, the definition is more specific. CEP is the radius of a circle centred on the target, at a specified range, in which 50% of the payloads impact. A smaller CEP means a tighter grouping around the aim point and a more accurate system. A larger CEP means rounds or measurements land farther from the target. The consolidated dual-use annex uses this weapons-accuracy form.

What the 50% radius tells you

CEP describes a typical result, not a worst case. Half of the measurements fall inside the stated radius, and half fall outside it. A CEP therefore says nothing about how far the outermost rounds may land. A buyer who needs a guarantee about the spread of every round must ask for a different measure or an additional requirement.

Because the circle is centred on the target, CEP is a single number that combines the spread of results into one radius. That makes it easy to put in a specification, and it is why the measure is common in guidance, navigation and weapons testing.

CEP in missile and munition accuracy

In weapons language, CEP is paired with a range. A system is described as having a certain CEP at a certain distance, because accuracy usually changes with range. Export-control texts use this pairing. One control covers systems capable of accuracy of 3.33% or less of range, and gives the example of a CEP of 10 km at a range of 300 km. The same wording appears in the annex to Regulation 2020/1749.

In that same body of text, CEP is also described as the "circle of equal probability." Both names refer to the same 50% radius.

Worked examples from weapons specifications

• 10 metres CEP: a U.S. Army description of a laser-guided mortar explains that rounds are expected to fall within a 10-metre-radius circle around the target 50% of the time. See the U.S. Army article on the precision mortar.
• Less than 50 metres CEP: a U.S. Army description of near-precision artillery rounds gives this figure as the target accuracy measure for the projectile guidance system. See the U.S. Army article on near-precision artillery.
• 10 km at 300 km: this equals 3.33% of range, as set out in the export-control example above.

Each example states a radius in a unit of distance. The radius is what the buyer is specifying, and the 50% probability is built into the term.

Terminology sources and the Canadian export list

NATO maintains NATOTerm, its official database of non-classified military and NATO-relevant terminology. It is the reference point for how allied military terms are used in English and French.

On the Canadian side, Global Affairs Canada publishes the Guide to Canada's Export Control List, which is the reference for goods and technology whose export is controlled.

What CEP means for a supplier bidding on Canadian public contracts

When a solicitation states a CEP value, it sets a measurable accuracy requirement. A bid team should read the number as a radius with a 50% probability, confirm the range at which it applies, and check that the supplier's own test data uses the same definition. A claim of accuracy that does not name the range or the probability does not match the way CEP is defined.

Suppliers that deal in guidance, navigation or missile-related technology should also review the Guide to Canada's Export Control List before quoting or sharing technical data outside Canada.