When you cut wood, it takes less space because it is easier to fill gaps. Apparent volume is then less.
For example, a stere of wood uses 1 cubic metre occupied by 1 metre long logs ; but you cut these logs in half, each of them will be 50 cm long, they will take a volume of about 0.8 m3 because it is easier to fill the gaps.

So there is an equivalence between various quantities of wood depending on log sizes, so you can compare prices according to size, or your provider can give logs of different sizes if he doesn't have enough size of ordered size (take care they still fit in your fireplace, stove or heating...).

When wood is humid, it is heavier. The norm is to dry wood for 2 years before burning it because green or humid wood has a poor energetic performance. It needs 18 months in a ventilated shelter to get a humidity of 20 %.

Fireplaces with inserts have a much better energetic performance than open fireplaces (and anyway, open fireplace pollutes 8 times more particles). Some areas want to regulate the use of open fireplaces.

The energetic power of dry wood per weight is about the same (4 kWh/kg at 20% humidity) for any kind of wood (including bark) but some wood is heavier so the energy quantity varies per unit of volume.
In Europe, the highest quality of wood includes a mix of 95 % of hornbean , oak and European beech, very heavy woods which burn slowly with a good ember.

With the following array, you can easily compute the equivalence between an invoiced volume in stere and the apparent volume. It also gives an equivalent weight and heat of combustion, so the energetic power of combustion.

As it is energy, it is also compared to petrol equivalent.

Enter a value in the second column of the following array and the conversion will be performed automatically in all other units.