How do you convert ppm to weight percent?

To convert ppm to wt%, you need to divide ppm with 1000000 to get to wt%.
For example:
If you have 4000ppm, it is the same as 0.004 wt%.

I dont agree with this answere.
Actually 4000ppm means 4000mg in 1Kg (1000g). Hence a simple solution is as under;
1000g contains 4000mg
or
1000g contain 4 gm. Hence 100g will contains 0.4 grams. This is the answere i.e. 0.4%

because % means amount present in 100 grams.

The first answer above should be:

To convert ppm to wt% (percent by weight), you need to divide ppm by 10,000.
For example:
If you have 4000 ppm, it is the same as 0.4 wt%.

If a lab result for the concentration of lead (Pb) in a paint chip sample is 10,400 ppm, the concentration in percent lead by weight is 1.04. If the result is reported as 1.04 % Pb by weight, then the concentration can be converted to 10,400 ppm.