The traditional Eclectic texts (Felter and Lloyd, 1898) typically recommend doses between 1-60 drops (where 60 drops is approximately 2ml).
I use anywhere between 5-60 drops of a herb and if in formula, I will often use, for example, 5 herbs compounded together each with 10 drops worth per herb, so 50 drops total twice per day. When you use more herbs, their effects often increase so usually less volume is required per herb. There are no strict rules on this stuff most of the time, and the best thing to do is use a good dose of common sense and some guidelines from text books/ traditional knowledge.
Small frequent doses (e.g. 3 times per day or 4) tend to be a lot stronger, but that isn’t certainly always desirable or a good thing. It is often better to err on the cautious side to begin with.
There are various schools of thought for dosing medicinal herbs that are described below:
Lower (ethereal) doses
The Matthew Wood school of dosing which is along the lines of John Scudder, an Eclectic physician (Scudder, 1870), uses small doses, 1-5 drops, between 1-3 times daily (Wood, 2004). Jim McDonald uses doses a little higher, between 5-15 drops, 3 or up to 5 times daily. Where more regular doses are used to give a stronger therapeutic effect.
I am not a fan of homeopathy because of the aggravation potentially causing serious problems. What I describe here with these lower doses does not appear to involve aggravations so it is not homeopathy. It is important not to rule out the low doses of herbs, they are far more complex than drugs, very different effects may be had at 5 drops instead of 60.
Higher (material) doses
There is the British Phytological School (Hoffman, 1988), where doses of a formula or herb usually range from 1-5ml, three times daily. This means 2 full droppers (25 drops each, 50 drops total) is approximately the starting dose, a little more than. If using a formula the overall dose will generally also be between 1-5ml. I generally find 3 times daily too much, but it varies based on person. I think the vata constitution requires less herb oftentimes.
Some herbs, like blue vervain or lobelia, only require very small doses so it does vary depending on herb sometimes
Dried capsule extracts
I often start with the directions on the packaging with the standard dose, but also get information from papers and text books.
I made these myself using an A. Vogel bottle or a dropper and a measuring cylinder. A dropper can be 20 or 25 drops, both end up around 0.70-75ml. Herb Pharm bottles say on the back 0.7ml per dropper.
1 dropper = 20-25 drops = approx 0.75ml
2 droppers = 40 drops = 1.5ml
4 droppers = 80 drops = 3ml
6 droppers = 120 drops = 4.5ml (which is about 1tsp) (generally approx max dose)
A drop and a dropper can be variable, many people are saying 20 drops is 1ml, this is approximately true as you can see above.
Felter, Harvey and Lloyd, John. King’s American Dispensatory, 1898.
Hoffman, David. Holistic herbal. Element Books, 1988.
Scudder, John. Specific Medication and Specific Medicines, 1870
Wood, Matthew. The Practice of Traditional Western Herbalism: Basic Doctrine, Energetics, and Classification. North Atlantic Books, 2004.