How spliffs and cannabis are counted

What does the calculator mean by a spliff?

The calculator asks about “spliffs (joints)”. One published definition describes spliffs as “joints (cannabis cigarette) filled with loose-leaf tobacco and cannabis” (Kumar et al, Scientific Reports, 2020). The calculator counts spliffs and joints the same, at 4 cigarettes each, whether or not tobacco was added.

How does the calculator count spliffs?

• One spliff counts as 4 cigarettes.
• Spliffs are entered as a number a day, with the number of years.
• The original calculator had one row for “Cigars or spliffs”. Version 2 asks about them separately, and both still count as 4.

Where does the figure of 4 come from?

The References page cites Aldington S et al, “Effects of cannabis on pulmonary structure, function and symptoms”, Thorax 2007;62(12):1058-63. It says: “This study suggested that the smoking effects of one spliff could be compared to between 2½ and 5 cigarettes. In the ‘pack year’ calculator we gave a figure of 4, i.e. the same as a cigar.”

The calculator’s 4 sits within that range of 2½ to 5.

How do I enter spliffs?

1. In the calculator, on “What have you smoked?”, tick Spliffs, and anything else you smoked regularly.
2. The step asks: “How many spliffs (joints) a day, and for how many years?”
3. Enter the number a day and the number of years. Use a decimal point for part years, for example 2.5.
4. If the amount changed, choose Add another period and enter each amount with its own years.

If you rolled spliffs with loose tobacco, count the spliffs only: do not enter that tobacco under Loose tobacco as well. Tobacco smoked on its own, in cigarettes or roll-ups, goes under its own type. Every figure here is approximate; what matters most is getting a number.

After the tobacco steps, an optional history step asks whether you still smoke, when you stopped and how many years you smoked in total. FAQ 2 recommends recording stopping dates and years smoked alongside pack years.

What do 2 spliffs a day for 10 years come to?

• 2 spliffs × 4 = 8 cigarettes a day.
• 8 × 10 years = 80.
• 80 ÷ 20 = 4 pack years.

If the same person also smoked 10 cigarettes a day over those 10 years, that adds 10 × 10 ÷ 20 = 5, giving 9 pack years in total. The calculator’s breakdown shows 5 for cigarettes and 4 for spliffs.

What happens after the result?

The result screen shows the total and a breakdown by type of tobacco. You can download or email a PDF, print the result, or save a link to it. Clinicians can also copy a line for the patient record.

What are the limits?

The References page says: “This is not an exact science and approximations have been made.” The figure of 4 applies to every spliff, whatever its size and whether or not it contained tobacco; the calculator does not ask about either.

The calculator records combustible smoking products only, so vaping is not counted (see the FAQs). Pack years are a record of past smoking, not a diagnosis. If you are worried about your health, speak to your GP practice or use NHS 111.