I think I have it. –> GC/MS Test at 15ng/ml cut-off for THC-COOH metabolite.

1 Joint Equation (explanation below the equation):

130,000,000 (ng in one avg joint) x .7 x.2 x.3 = 5,460,000ng

5,460,000 / 2,400 (ml of urine in 30 hour period) = 2,275ng/ml

2,275 x .3 x .3 = 252ng/ml (after 60 hours)

252 x .67 x .67 = 112ng/ml (after 120 hours)

112 x .8 x.8 = 71ng/ml (after 180 hours)

71 x .9 = 63ng/ml left in your system – but in that 30 hour period (180-210) you’re only eliminating 8ng/ml each time you pee – so you pass at this point.

The reason the elimination goes from 2/3 to 1/3 to 20% to 10% is because as time moves forward you’re eliminating less from first pass and more from your fat cells.

Explanation of Equation:

1 joint = 1 gram which equals 1,000 milligrams or 1,000,000,000 nanograms. Today’s Marijuana contains approximately 13% THC on average. So, a joint would contain 130,000,000 nanograms of THC. When smoking approximately 30% of the THC is destroyed in a process called pyrolysis (it burns). So, that leaves you with 91,000,000 nanograms. Only 20% of the THC is filtered out through the urine, so that leaves you with 18,200,000 nanograms. Only 30% of the THC in your urine will be the metabolite THC-COOH, so that leaves you with 5,460,000 nanograms in your system. (Some studies say we should cut the number in half because 50% of the THC is lost in side-stream smoke, but let’s assume you’re a really efficient smoker to be safe.)

Now, we’ll get into the elimination. I’m breaking our time period down into 30 hour increments. The average person urinates 2000ml in 24 hours, which makes approximately 2,400ml in 30 hours. We’re looking for ng/ml so we’ll divide 5,460,000 by 2,400 = 2,275ng/ml.

In the first 30 hours you’ll eliminate 2/3. You’ll be left with 758 ng/ml, but you’ll eliminate at roughly 1,517 ng/ml throughout the day (2275 minus 758). The next 30 hours you’ll eliminate 2/3 again. You’ll be left with 252ng/ml and eliminate at 506 ng/ml throughout the 30-60 hour period after smoking.

In the next 60 hours you’ll eliminate at 1/3 every 30 hour period. So, 252x.67=168ng/ml left in your system, and peeing at 84ng/ml in hours 60-90. Then, you’ll have 112 and pee at 56ng/ml in hours 90-120.

In the next 60 hours you’ll eliminate 20% per 30 hour period. So, 112x.8=89ng/ml left in your system, and peeing at 23ng/ml in hours 120-150. Then, you’ll have 71ng/ml in your system in hours 150-180 at pee at 18 ng/ml.

From then onward you’ll eliminate 10% per 30 hour period. So, 71x.9=63ng/ml and you’ll eliminate at 8ng/ml. You should be clear at this point (hour 180 / day 7.5) so long as it was only one gram, it was average marijuana, and it was a single-use. You can continue on the formula if you want to see when it will be almost completely out of your system…just keep multiplying by .9.

Single Puff:

If you only took one hit then in the beginning of the equation you can divide by 20. An example of a one hit equation below:

130 million ng / 20 = 6.5 million ng. 6.5million x .7 = 4,550,000 x .3 = 1,365,000 x .2 = 273,000ng. Divide ngs by 2,400ml = 113ng/ml. Multiply 113 by .3 = 34 (eliminate at 79). 34 times .3 = 10.2 (eliminate at 24 in hours 30-60). Then 10.2 times .67 = 7ng/ml (eliminate at 3ng/ml in hours 60-90) You’re in the clear at least by hour 90 with one toke. -Carl Miller