wGRP — weighted rating, and how it differs from GRP

wGRP (weighted GRP) is GRP normalised to a base spot length and adjusted for placement conditions. wGRP is usually the figure a contract's commitments are written in.

Why weighting was needed

A five-second spot and a forty-five-second spot in the same break earn the same raw rating: the break has one audience. They take up very different amounts of airtime, though, and they cost differently. Weighting converts them into comparable units.

How it is calculated

A standard spot length is taken as the base — on most markets 30 seconds, with a coefficient of one. Other lengths get a coefficient relative to that base, and the airing's rating is multiplied by it:

wGRP = GRP × length coefficient × position coefficient

The second multiplier appears wherever a channel charges for position within the break: first and last are more noticeable than the middle, and that too becomes a coefficient. The actual values are the broadcaster's — they are part of the rate card, not a universal constant.

Why it matters in practice

If the contract names one measure and the report calculates another, an argument about whether the commitment was met is guaranteed. Which one the campaign goal is fixed in — GRP or wGRP — is worth checking before the first airing rather than after.

In OpenMediaLogic the broadcaster's coefficients are set in the system, so the plan and the post-buy are calculated by the same rules.