Approximately 3' x 5'
From the Revolutionary War - Washington's Cruisers Flag - “An Appeal to Heaven".
"An Appeal to Heaven" flags were first flown over six cruisers, which were commissioned under General George Washington in 1775. The large Eastern White Pine, depicted on the flags, was a highly desirable tree for use in building ship masts.
England therefore enacted "The Mast Preservation" clause in order to reserve the best trees for itself. If an American Colonists desired to harvest a tree on his property, he would now have get the King's Surveyor to first inspect his trees. The trees suitable for building ship masts were then marked with a broad arrow by the surveyor, signifiying them off limits to the land owner. The Colonist would then need to purchase a royal license from the crown to harvest any trees on his lot.
These requirements caused such ire among the Colonists, that it helped to spark the American Revolution. It was no coincidence that the flags were flown atop the Colonists' warships - the very thing for which England sought after them! The flags also served as a constant reminder to the sailors of the wrongs commited against them by the Crown.