Unmeasurable means, specifically not able to be measured
objectively. We use this one in the literal sense: “the immense lizard was
unmeasurable with the tiny ruler in the standard lizard measuring kit”; “the
sea trench in which the angler fish lived was of an unmeasurable depth”.
Immeasurable means, a bit less specifically, too
large, extensive or extreme to measure. We should reserve this one for the more
figurative sense (otherwise there’s no point in having two different words): ” the immeasurable mercy of their god”;
“he had immeasurable ambition”.
