Is this less than a one year overstay since left voluntarily before the one year anniversary of the I-94, so a three year ban? Or does the overstay start from the termination of employment making it more than a year, so a ten year ban?
It depends on a few factors, including (1) what it says on your I-94, (2) the dates when you overstayed - USCIS published a new policy in 2018, (3) whether the pending court cases regarding the new policy are settled in favour of USCIS and if so, what the effective date ends up being for the new policy, (4) whether there is any mail from DHS you might have missed.
This is a complicated area of the law and it is best to consult with a lawyer.
Is there any way to check with the embassy or USCIS to see what the ban is?
The general answer to this kind of question is: the only way to know for sure whether DOS considers you to have a 3- or 10-year bar is to apply for a visa. The only way to know for sure whether DHS considers you to have a 3- or 10-year bar is to apply for admission. If the visa or admission is refused with the code 212(a)(9)(B)(i)(I), then you have a 3-year bar. If the code is 212(a)(9)(B)(i)(II), you have a 10-year bar.
Or maybe they are not even aware of the overstay so this would be a bad idea, telling them about it.
Note that when you apply for a visa, you are required to answer "yes" to the question asking whether you ever overstayed your status or otherwise violated the terms of your admission during any previous travel to the US, and you will have to provide an explanation. DOS will then determine whether a bar exists.
Finally, keep in mind that even if you don't have a statutory bar, the overstay will weigh heavily against you in future visa applications (i.e., as evidence that you might overstay again or attempt to live in the US permanently).