There are some cases where higher doses are surely preferred and vice versa, but our current understanding is low and high dosing of many herbs both work. It seems to be more about matching the person with the herb. Quality of the herbs is very important. Generally, either fresh tinctures or those freshly dried are preferred, but this is not always the case. Many companies are not interested in these details.
The traditional Eclectic texts (Felter and Lloyd, 1898) typically recommend doses between 1-60 drops (where 60 drops is approximately 2ml). I personally think it is usually best to start with lower dosing, only using the high dosing method where necessary. Low and more frequent dosage is my primary method (e.g. 5-10 drops per herb, 3 times per day). Then I will often use, for example, 6 herbs compounded together each with 5 drops worth per dose, so 30 drops total.
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.
Higher (material) doses
There is the British Phytological School (Hoffman, 1988), where doses usually range from 1ml to 5ml, three times daily. This means 2 full droppers (25 drops each, 50 drops total) is approximately the starting dose, a little more than. Some herbs, like blue vervain or lobelia, only require very small doses so it does vary.
Dried capsule extracts
I often start with the directions on the packaging, 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.