Can I measure the object with accuracy of 3-4mm to measure both length and circumference.

Yes. You get a tape measure…
Oh you mean can you do it with the decawave parts

In all seriousness while UWB systems can get that accurate with enough anchors and averaging it’s very tricky. There are almost certainly far better approaches that will be simpler and/or more accurate.

Hi Thanks for response.
is there any equation formula which gives some rough estimate, on how many anchors to be connetced and at what distance to achieve this accuracy.

Object will come to a stationary position for length and circumference measurement.
So anchors can be placed on top/bottom/sideways of object and on object too they cna be placed.