We are given number in words " two hundred fifty three thousandths".
Let us write it in number form: First we would write the number form of "two hundred fifty".
Two hundred fifty = 253.
Now, we need to write three thousandths.
Three thousandths = .003
Now, we need to combine 253 and 0.003.
On combining we get 253.003.
Therefore, two hundred fifty three thousandths in standard form is 253.003.