What SKS says. The power level of bound spells equals the casting value of normal spells, i.e. the value that has to be equalled or excelled by the total casting result of the dice (+ any boni, like Wizard level). .
BRB p. 28: "At the start of each Magic phase, the casting player determines the strength of the Winds of Magic by rolling 2D6."
To these are added dice from channeling (e.g. from Wizards & Warrior Priests). This is the power pool.
Note that the "casting player's power pool can never exceed 12 dice at any point in the phase — any dice generated beyond this number are lost. "
BRB p. 32: "Each spell has an associated casting value, any number from 3 upwards. Spells with a higher casting value have greater effect, but require more power"
"If the casting result equals or exceeds the spell's casting value, the spell is cast (though it may be subsequently dispelled and neutralised by the opposing player...).
BRB p. 37: "The required casting value is equal to the bound spell's power level."
