Sources:
Post by Conner Davis in "How can I work out how many small circles I can fit into a big circle?" on Quora

You can roughly estimate the area effect of a bomblet weapon through this equation:

Where

R: Area Effect Radius of Weapon (meters)
N: Number of Bomblets
A: Area Effect Radius of Individual Bomblet (meters)
P: Packing Efficiency

P is 12 if you're assuming perfect efficiency in placing each individual bomblet where it can maximize area covered.

In the real world, P is much lower. Some public examples are:

155mm M483A1 ICM Round: Armies of NATO’s Central Front by David C. Isby gives the lethal area of a 155mm ICM round as 25,800 ft2 (55m diameter). The M483A1 round had 88 x M42/M46 grenades; each with a lethal radius of 10m. Using the above formula, I get a P of around 0.1 for conventional cargo artillery shells.

MGM-140A ATACMS Block I: This variant has 950 x M74 APAM Bomblets, each of which has a lethal antipersonnel radius of 15m, according to FM 6-60 (1996). Up until 2024, it was publicly admitted to have an area coverage of 33,000 m2 (205m diameter), giving a P of 0.025. On or around 1 May 2024, a major strike was executed on Luhansk where ATACMS was seen to have a bomblet pattern of about 340m diameter (90,792 m2), giving a P of 0.185.

I feel that for advanced weapons like ATACMS which utilize an electronic fuze to begin dispersal of bomblets, P can be varied according to operator need.

For example, if there's low levels of EW (low degradation of GPS); or the operator wishes to strike a relatively constrained point target to limit collateral damage; they can program ATACMS to lower the altitude at which bomblet dispersal begins; reducing the size of the affected area (and increasing lethality within the area).

Alternately, if there's high levels of EW (high degradation of GPS); or there's an extremely large area target, ATACMS can be detonated at a higher altitude, giving the bomblets more time to spread. The major downside would be significantly reduced lethality over that target area, but it would be useful in some instances for "harassment fire".

If there's such a capability within the ATACMS system, appropriate P levels would be 0.20 to 1 depending on the operator's targeteering criteria.