Infusion calculator: herb to oil ratios, real yield and losses
Work out how much dried herb and oil an infusion needs, how much oil the herb keeps, what you actually get back, and what that means for a salve at a set botanical strength.
Infusion recipes are written in cups and handfuls, and they never mention the part that actually decides your batch size: the herb keeps a large share of the oil. Weigh 60 g of dried calendula into 600 g of sunflower oil and you will not get 600 g back. This tool works the shortfall out first, so the salve you planned is the salve you can fill.
Dried botanicals hold roughly 1.5 to 3 times their own weight in oil after draining, and about 1 to 1.5 times after pressing. At a common 1:10 herb to oil ratio, expect to recover around 80 to 88 percent of the oil you started with. Plan the infusion from the oil you need at the end, not the oil you pour in.
Plan an infusion
Infuse dried material only. Fresh plant carries water into an anhydrous product, and water is what turns a salve mouldy. If you must use fresh material, wilt it for 24 to 48 hours first and accept a shorter shelf life, as mould in balms explains.
Why the yield is never what the recipe says
Dried plant material is porous. It takes up oil into the cell walls and the spaces between them, and only some of that comes back out when you strain. The retention depends on the structure of the material rather than the species: light petals hold the most oil per gram, roots and barks the least, powders least of all until they clog the cloth and cost you oil a different way.
| Material | Oil retained | Practical effect |
|---|---|---|
| Calendula and light petals | 2.2 to 2.8x | The classic surprise: 50 g of petals can keep 130 g of oil |
| Dried leaf and flower mix | 1.8 to 2.2x | The default assumption for most salve herbs |
| Chopped leaf, comfrey, plantain | 1.5 to 1.9x | Denser material, drains faster |
| Root, bark and seed | 1.2 to 1.6x | Low retention, but needs a longer or hotter infusion |
| Powder and resin | 1.0 to 1.3x | Retention is low, filtration loss is high |
Squeezing recovers roughly a third of what a simple drain leaves behind, and a press recovers rather more than half. It is not free: the harder you press, the more fine sediment and plant water you push through with the oil, and sediment at the bottom of a jar of infused oil is a spoilage site. Filter pressed oil through a coffee filter or fine cloth and let it settle for a day before you decant it, which the infused oils page covers in more detail.
Ratios, and what they buy you
A ratio is a statement about concentration, not about quality. Doubling the herb does not double the useful extract, because the oil saturates and because most of the interesting constituents of a salve herb are only sparingly oil soluble in the first place. The practical band is 1:5 for a deliberately strong infusion and 1:20 for a scented, gently coloured one; 1:10 by weight is the honest default.
Two habits protect the batch. Weigh, never measure by volume: dried herb varies in bulk density by a factor of three, so a cup of calendula and a cup of chopped comfrey are not comparable amounts. And infuse into an oil that will survive the process, which means a stable, high-oleic carrier rather than a delicate one, for the reasons set out in rancidity and oxidation.
Infuse 10 to 15 percent more oil than the calculator asks for. The extra covers the drips, the last of the marc and the sediment you decide not to decant, and it costs almost nothing.
Heat, time, and what the method changes
Three methods dominate, and they differ in what they extract and what they damage. A cold or solar infusion of two to six weeks is gentle, keeps volatile aroma, and asks for scrupulous dryness because it spends weeks at room temperature. A warm infusion at 40 to 60 C for four to eight hours is the working compromise: fast enough to make in a day, cool enough to leave the oil intact. A hot infusion above 70 C is quick but oxidises the carrier and drives off aroma, and it is only sensible for roots and barks.
Whichever you choose, the shelf life of the infusion follows the carrier oil, not the herb, with a small penalty for the plant material and any moisture it brought with it. Date the jar, keep it dark and cool, and use it inside the carrier's own window; the shelf life calculator will put a figure on it.
Frequently asked questions
How much oil does dried herb really absorb?
Between about 1.5 and 3 times its own weight, depending on the material and how hard you strain. Light petals such as calendula sit at the top of that band, roots and barks at the bottom. It is the single largest source of a short batch, and it is why infusions should be planned backwards from the oil you need.
Should I use fresh or dried plant material?
Dried, for anything anhydrous. Fresh material carries water, and water in a salve is what allows mould to grow. If you infuse fresh herb, wilt it for a day or two first, watch for cloudiness or a layer at the bottom, and treat the oil as short dated.
Is a solar infusion better than a warm one?
Not better, different. A cold or solar infusion keeps more of the volatile aroma and puts less thermal stress on the oil, but takes weeks and needs a scrupulously dry jar. A warm infusion at 40 to 60 C for a few hours extracts more in less time and is easier to keep clean.
What ratio should I use for calendula?
Start at 1:10 by weight, dried petals to oil. Below 1:5 the marc is hard to keep submerged and the yield falls sharply, and above 1:20 the colour and character are faint. Weigh rather than measure by volume, because petals are extremely light for their bulk.
Does infusing shorten the shelf life of the oil?
Slightly. The carrier still sets the limit, but plant material adds traces of moisture, sediment and pro-oxidant metals, so treat an infusion as a little shorter lived than the plain oil. Store it dark and cool, and keep sediment out of the jar you formulate from.
Can I infuse a butter instead of an oil?
Yes, at a temperature that keeps it liquid, though it is harder to strain and the yield is worse because the butter sets in the marc as it cools. Most makers infuse a liquid oil and blend the butter in afterwards.
Sources and further reading
- American Herbal Products Association, Botanical Safety Handbook, 2nd edition, CRC Press.
- European Directorate for the Quality of Medicines, European Pharmacopoeia general monograph: Herbal drug preparations, Strasbourg.
- Committee on Herbal Medicinal Products, Assessment report on Calendula officinalis L., flos, European Medicines Agency.
- Food and Agriculture Organization, Small scale oilseed processing and oil recovery, FAO agricultural services bulletins, Rome.
Reviewed and updated 6 September 2026. Spotted an error? Tell us and we will fix and log it.