3 tons how many metric meters does this work out to be

Metric Meter is not a relatable unit to tons. Cubic meter might be what you are looking for.
That being the case it depends on what you have 3 tons of, everything has a different density, meaning everything has a different weight(tons) per unit of volume(cubic meter) so first off you need to find out what material you are trying to figure this out for. Water for example weighs less per cubic meter than steel weighs per cubic meter. Then once you know that material you can then ask what is the density of that material. Once you find the density you can convert that information into any relative unit of measure you need, so re-post with a little more info and make sure you are looking for the right units and somebody can answer your question.
Sorry I couldn't be more help.