BHow to Calculate Ppm for a Fertilizer?

Yes, I've ordered a TDS measuring wand, but in the meantime...

There must be a formula to calculate ppm when using a fertilizer.
Case in point:

I have FF Grow Big (6-4-4) and if used as directed, adding 1 teaspoon full per gallon (assume neutral/distilled water) how many ppm of the three nutrients would be in the gallon?

If pressed (ie, a final answer on Jeopardy) I would guess one figures out the "weight" of one teaspoon full then calculate 6% of that and the "weight" (volume?) of the water and do the math... But I also thought there might be a calculator or converter online.

Does anyone know or have a link?

thanks

http://www.firstrays.com/fertcalc.htm Save the page it works from your download folder save as html complete.