There are infinite chants dedicating merit, some brief and some long. This is from the Theravada Forest Monk tradition:
May all beings always live happily,
free from animosity.
May all share in the blessings
springing from the good I have done.
“Brief Notes on Dedication of Merits” according to Vajrayana Mani Mantra Teachings as told by the Venerable Yangthang Rinpoche Penor Rinpoche
The dedication of merit as it is taught in the Buddhadharma is one of the most vital and profound part of spiritual practice and a unique aspect of the Buddha’s teachings not found in other forms of spirituality. The reason why we are still suffering in samsara is that we have not gathered the accumulations of merit and wisdom. Although we have performed numerous positive deeds over many lifetimes – we have never dedicated this merit to the achievement of full enlightenment for all sentient beings. Thus when the positive karma ripens, it simply leads to some temporary positive states or happiness which will be used up in time and therefore when our merit finishes, we will lose that happiness and simply fall back into suffering.
By dedicating our merits to supreme awakening for all beings, we will experience positive results and well-being from that merit, plus it will not be used up until the ultimate aim of your dedication, which is supreme enlightenment for all beings, is achieved. Thus, dedicating our merit is like adding a drop of water to an ocean, just as the ocean never dries up, that drop of water is never exhausted. The ocean is likened to the vastness of the purpose to which our merit (a drop of water) is directed to.
Another reason why we dedicate our merits is because in the teachings it is said that ‘a hundred eons of generosity and moral discipline can be destroyed in one moment of anger’.