40% CBD oil: 16 to 20 mg per drop, the maths

The percentage is the proportion of CBD in the oil. Most sellers use 40% to mean 400 mg per millilitre, so 4,000 mg in 10 ml and 12,000 mg in 30 ml. The remainder is a carrier oil, often medium-chain triglycerides (MCT), olive oil or hemp seed oil.

The figure is still easy to misread, because a percentage can be by weight or by volume and labels rarely specify which. Divide the total in mg by the volume instead: 4,000 mg in 10 ml gives 400 mg/ml whichever way the percentage is expressed. When the label states no total in mg, "40%" is too vague for any precise calculation.

Look at the word "spectrum" as well. A full-spectrum oil retains the other hemp compounds, a little THC under the 0.30% limit among them, while an isolate-based oil contains CBD alone. The difference is explained in our definition of full spectrum and our comparison of full spectrum and isolate.

Everything depends on how big a drop is. According to the Food Standards Agency (FSA), the UK food regulator, 10 mg of CBD is about 4 to 5 drops of 5% oil. At 50 mg/ml for a 5% oil, that puts one drop at 2 to 2.5 mg and the dropper at 20 to 25 drops per millilitre. The table uses the same dropper for the other strengths.

These figures are estimates. The size of a drop varies with the dropper tip, the viscosity and temperature of the oil, and the angle of the bottle. At 40% the margin of error is large, since a slightly bigger drop adds several milligrams. A graduated syringe gives more precision: 0.1 ml of a 40% oil holds 40 mg of CBD, and 0.05 ml holds 20.

Two authorities give a figure for CBD in food. On 9 February 2026, EFSA set a provisional safe level of 0.0275 mg per kilo of body weight per day, roughly 2 mg for an adult of 70 kg. The level covers only CBD of at least 98% purity. The agency could not establish safety for people under 25, pregnant or breastfeeding women, or people taking medication. Since October 2023, the UK FSA has advised against going above 10 mg a day.

A single drop of 40% oil equals 8 to 10 times EFSA's daily reference and 1.6 to 2 times the FSA's. Staying at 2 mg would require a tenth of a drop, and no dropper delivers that. The format's practical limit lies there: with so much CBD in so little liquid, a small amount cannot be measured in drops. Our article on how much CBD per day explains the origin of these references.

None of these figures is a recommended dose. Epidyolex, the only authorised CBD medicine, is a 100 mg/ml solution prescribed under medical supervision for rare forms of epilepsy. A 40% oil is four times as concentrated and comes with none of those controls. CBD interacts with some medicines, so ask a doctor or a pharmacist if you are on any treatment.

A high strength printed on the label is no guarantee of the contents. In 2023 a UK team tested 29 CBD oils bought in the UK. Only 5 held the stated amount to within 10%, 23 held less, and one held 50% more. In France, the addiction monitoring study run with Lille University Hospital looked at ten products bought in pharmacies, mostly oils, and found a CBD level matching the label in only one case out of two.

For an oil, three lines of a certificate of analysis matter. The first is the CBD concentration in mg/ml, which you compare with the stated total. The second is the Δ⁹-THC, capped at 0.30% of the product; at 0.2%, one gram of oil contains 2 mg of THC. The third is the batch number, which has to match your bottle. Our guide to reading a certificate of analysis goes through each line, and the measurement methods are described on the laboratory page.

The traces of THC in a full-spectrum oil can also count at the wheel. What these tests detect is explained in our guide to saliva drug tests.

Bottled or in capsules, a CBD oil meant to be swallowed counts as a food. It comes under Regulation (EU) 2015/2283 on novel foods, which lets only authorised foods onto the market, and no CBD-based ingredient has been authorised.

France's agriculture ministry set out its position on 20 May 2026: foods containing CBD are not authorised, food supplements included, and checks now extend to every sales channel. Hemp seeds and their derivatives, such as hemp seed oil, are the only exception, provided they are not enriched with cannabinoids. The strength is irrelevant: a 5% oil to swallow is covered exactly as a 40% oil is.

An oil sold for the skin comes under another text, the EU cosmetics regulation, and may not be presented as something to swallow. The timeline is set out in our overview of CBD regulation in 2026. The oils in our catalogue are grouped in the CBD oils category; their stated strengths run from 5.1 to 19.6%, so none reaches 40%.