Actually, I know that one ounce (weight) of ground flax seeds measures approx. 3½ Tbsp (volume) because I have a scale, and I've measured it

The volume measure for WHOLE seeds is less, since they're more compact ... a bit less than 3 Tbsp per ounce, in my experience.

Since this member wishes to use such a small volume as 1 teaspoon, it would be very impractical to try to weigh it (unless the scale measures in 5-gram increments).

You make a good point though about the accuracy of measuring solids by volume, which is "iffy" at best. One cup of broccoli can be more or less depending on the size of pieces it's cut into; weighing is much more accurate.

Doreen