Aroma Corner
essential oils at home, with care
Blending factors: how many drops of each essential oil to use
Put equal drops of peppermint and sweet orange in a bottle and you will smell peppermint and not much else. Oils differ hugely in strength, so a blend made drop for drop tends to be ruled by its loudest member. Blending factors are an old rule of thumb for evening this out.
What a blending factor is
Each oil gets a number, usually between 1 and 10, that stands for how large a share of a blend it can take before it takes over. A high number means a mild oil that can have a generous share: bergamot is traditionally given 10 and lavender 7. A low number means a strong oil that needs a small share: peppermint, ginger and patchouli all get 1.
The factor is a share, not a drop count. It tells you how to divide drops between oils, never how many drops to use in total; that comes from your dilution. Nor is it a safety limit for any single oil.
The figures circulate in aromatherapy textbooks and course notes. They come from experience rather than measurement and sources differ, so where another figure is often quoted, the table says so. Treat them as a starting point for your nose.
Traditional blending factors
| Oil | Factor | Notes |
|---|---|---|
| Benzoin | 1 | Thick, vanilla-like resinoid, often sold already diluted |
| Bergamot | 10 | Choose FCF (bergaptene-free) for skin |
| Black pepper | 1 | Some books give 2 |
| Cardamom | 1 | Sweet spice with a fresh edge |
| Cedarwood | 3 | Dry, quiet base note |
| Chamomile, roman or German | 1 | Some books give 2; daisy-family allergy |
| Clary sage | 4 | Often left out in pregnancy |
| Cypress | 5 | Clean forest scent |
| Eucalyptus | 1 | Not for young children |
| Fennel, sweet | 1 | Some books give 2; avoid in pregnancy and with epilepsy |
| Frankincense | 3 | Keep the cap tight, it oxidises |
| Geranium | 3 | Rosy and easy to overdo |
| Ginger | 1 | Warm, peppery root |
| Grapefruit | 4 | Cold-pressed oil is mildly phototoxic |
| Jasmine absolute | 2 | Some books give 1; can cause skin allergy |
| Juniper berry | 4 | Fresh and gin-like |
| Lavender | 7 | The usual backbone of a blend |
| Lemon | 3 | Cold-pressed oil is phototoxic |
| Lemongrass | 1 | Irritates skin unless kept low |
| Marjoram, sweet | 3 | Warm herb |
| Melissa | 1 | Costly, often adulterated; keep it low on skin |
| Myrrh | 1 | Some books give 2 |
| Neroli | 2 | Some books give 4 |
| Patchouli | 1 | Earthy and long-lasting |
| Peppermint | 1 | Some books give 2; not near young children's faces |
| Rose absolute | 2 | Some books give 4 |
| Rose otto | 1 | Some books give 3 |
| Rosemary | 2 | Avoid with epilepsy and in pregnancy |
| Sandalwood | 6 | Soft, long-lasting base |
| Sweet orange | 3 | Not phototoxic, but oxidises quickly |
| Tea tree | 3 | Old, oxidised oil irritates skin more |
| Ylang ylang | 4 | Keep it low on skin |
The method, step by step
- Work out the total number of drops from your dilution. Droppers vary, but the usual rule of thumb is that 20 drops make about 1 ml. The practical dilution chart explains which strength suits which use; most adult body oils sit at 1 to 2 percent.
- Choose two to four oils and look up their factors.
- Add the factors together.
- Divide the total drops by that sum.
- Multiply each oil's factor by the result.
- Round every answer down to whole drops, then hand out any drops still missing, one at a time, to the oils with the biggest leftover fractions. The final total must match step 1, never exceed it.
- Mix the neat oils in a small glass bottle, smell the mix on a paper strip, then add it to the carrier and label the bottle with the oils, drops and date.
| Carrier | 1 percent | 2 percent |
|---|---|---|
| 10 ml | 2 drops | 4 drops |
| 30 ml | 6 drops | 12 drops |
| 50 ml | 10 drops | 20 drops |
Worked example 1: a 30 ml massage oil at 2 percent
The oils are lavender (7), sweet orange (3) and frankincense (3).
- Total drops: 30 ml at 2 percent is 12 drops.
- Sum of factors: 7 + 3 + 3 = 13.
- Divide: 12 ÷ 13 = 0.92 (to two decimal places).
- Multiply: lavender 7 × 0.92 = 6.44; sweet orange 3 × 0.92 = 2.76; frankincense 3 × 0.92 = 2.76.
- Round down: 6 + 2 + 2 = 10, so two drops are missing.
- The biggest leftovers are sweet orange and frankincense (0.76 each), so each gets one more drop.
- Result: lavender 6, sweet orange 3, frankincense 3. Total 12.
Worked example 2: a 50 ml body oil at 2 percent
A fresh, warming oil for the legs after a long walk: grapefruit (4), juniper berry (4), rosemary (2) and ginger (1).
- Total drops: 50 ml at 2 percent is 20 drops.
- Sum of factors: 4 + 4 + 2 + 1 = 11.
- Divide: 20 ÷ 11 = 1.82.
- Multiply: grapefruit 4 × 1.82 = 7.28; juniper berry 4 × 1.82 = 7.28; rosemary 2 × 1.82 = 3.64; ginger 1 × 1.82 = 1.82.
- Round down: 7 + 7 + 3 + 1 = 18, so two drops are missing.
- The biggest leftovers are ginger (0.82) and rosemary (0.64), so each gets one more drop.
- Result: grapefruit 7, juniper berry 7, rosemary 4, ginger 2. Total 20.
Seven drops of grapefruit in 50 ml is 0.7 percent, well under the 4 percent that Robert Tisserand and Rodney Young suggest in their book Essential Oil Safety as the most cold-pressed grapefruit should reach on skin that will see the sun.
When the arithmetic and safety disagree
Factors know nothing about the limits of individual oils. Take 30 ml at 2 percent (12 drops) of bergamot (10), lavender (7) and cypress (5). The sum is 22, and 12 ÷ 22 = 0.55, so the method gives bergamot 5 drops, lavender 4 and cypress 3. Five drops of bergamot in 30 ml is about 0.8 percent. For ordinary cold-pressed bergamot on skin that will be in sunlight, Tisserand and Young suggest no more than 0.4 percent, which in 30 ml is 2 drops. Use bergamot FCF instead, keep the oiled skin out of the sun for 12 hours, or save the blend for a diffuser. Lemongrass, ylang ylang, jasmine and melissa also have low skin limits; the essential oil dictionary lists cautions oil by oil.
Small bottles
A 10 ml roller at 1 percent holds only 2 drops, which cannot be split three ways. Instead, make a small stock bottle of neat oils using the factors themselves as drop counts (for example, lavender 7, sweet orange 3 and frankincense 3), shake it, label it, and take 2 drops of the mix for each roller. The guide to oils that blend well together uses the same trick. And trust your nose: the numbers get you close, and moving a drop from one oil to another is fine as long as the total stays the same.
Before you use a new blend
Patch test it first: rub a little of the diluted oil on the inside of your forearm and wait 24 hours. If the skin turns red, itchy or bumpy, wash it with mild soap and water and do not use that blend. Ask a doctor, midwife or pharmacist before using blends in pregnancy, on children, or if you have epilepsy or asthma or take regular medicines. Swelling of the face or lips, or trouble breathing, after using any oil needs emergency help.