Wood can not be measured very accurate by guessing on two similar sized wood pieces. Get a 20 gallon tub or close to it and carefully fill it with water to a fill line that is below the top. Then measure exactly a one or one and a half cubit feet of water and pour it into the tub and note the exact level of water in the tub and mark it. Grab a piece of wood and submerge it under water and when the water comes to the one cubic foot mark on the tub you have measured a one cubic foot piece of wood. Of course you will need to let it dry or weigh it before submerging. The other option is cutting a exact piece of wood square. Thanks
My point is, wood is not always consistent, even within the same tree. The ratio of wood fiber, air, moisture and pitch is not consistent in every piece of wood. Sap wood vs heartwood, not the same.