You can find a needle gauge at most stores that sell yarn, including walmart, or joanns, michaels, ac moore, hobby lobby. They're usually only about $2 and have holes with the US and metric sizes, sometimes with the UK size marked too.
Most chopsticks are size 8 or 9, sometimes 7 if they're thinner. Skewers would be about a size 2 or 3 I think, maybe 4. If you can't find a gauge, you can poke a neat hole in some paper and measure across it with a metric tape measure. Then use this chart
to see what the size is in US terms.