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Essential Oil Conversion and Measurements 5-31-08
by Sherrill Pociecha and Gary Bourbonais
"Help, I'm going crazy. I know 15 ml = 1/2 ounce, then again does it, or was it 1 cc = 1 ml = 20 drops, then again 1 oz = 30 ml. So 5/8 drams = what????"
If that heartfelt cry sounds familiar to you, read on!
Most people go through life with a false sense of security when it comes to weights and measures. But when you start dabbling in essential oils, it doesn't take long to realize that something's wrong with the whole picture. We've written this little Guide to the Seamy Side of Ounces, Drams and Drops in hopes that it might spare you a few of the more horrific measurement nightmares.
Learning to use essential oils (EO's) safely and effectively requires learning how to measure them for proper dilution. Beginners in Aromatherapy (AT) find themselves dealing with milliliters and ounces, teaspoons and tablespoons, drops and percentages, even upon occasion with the mysterious dram! They find themselves faced with this mixture of measuring systems when buying EO's and Fixed Oils (Carriers), and it can be confusing to figure out what is what, when and why. My personal opinion (and that of many others) is that things are all going to settle down nicely with the metric system of measurement sooner or later, but until then …
A Quick And Simple Measurement Approach
A few abbreviations used in this approach:
Note: TBS and tsp refer to the measurement kind that is used in the kitchen for cookery, not the kind you eat with. And: these are all measurements of volume or capacity, since EO's and carrier oils are liquids in most cases. Don't think of them as weights - EO's have different densities, but if you measure them in terms of volume everything stays consistent.
Note 2: Some people - not us! - use "gtts" as an abbreviations for "drops". You can too, if it makes you happy ...
The Conventional Rules of Thumb for Diluting EO's:
These conventional rules of thumb are not exact, but they are easy to remember and to calculate - which is worth a lot in this world!
Rough and Ready Conversions
These conversions are not exact, but they give you a starting point if you aren't familiar with ml:
1 oz = 30 ml (hm - see below if you want the gory details)
1 tsp = 5 ml
1 TBS = 3 tsp = 15 ml
1 ml = 20 drops (hm again! see below for more gory details)
You can put these all together and use a little simple math to switch back and forth between the systems:
1 tsp = 5 ml = 100 drops
3 tsp = 1 TBS = 15 ml = 1/2 oz = 300 drops
If you're using a recipe that calls for 15 drops of EO per TBS of Carrier, you know you have a 5% dilution, because you have 15 drops in 300 drops, which is 5%.
Or you wanted to make a 3% dilution for one ounce of massage oil, you would add 18 drops to the ounce (because .03 x 600 drops = 18).
A Note to Bottle-Shoppers:
The Gory Details
The section below is only for people who feel a craving to know exactly what's going on in the eerie world of EO measurements. If it confuses you, don't be alarmed! It really is confusing!
Q: How many drops are really in a ml?
Sherill says: It varies, depending on how dense the oil is and how big the dripper you're using is. The myth that 20 drops of eo = 1 ml is commonly used among aromatherapy authors, and it works well enough if you're blending in small quantities just for your own use. But when you get frustrated enough to spend a few hours counting drips, you'll find that most eo's are 25 or 30 drops per ml.
Gary says: If you want more precision, you might want to consider pipettes. These are kind of like long skinny eyedroppers (usually without the bulb to squeeze) and they are graduated with marks so you can truly measure accurately what you are dispensing. A one ml pipette (often this size is known as a serological pipette) graduated to tenths of a ml, or better yet to hundredths, is ideal. Using these I can make my drops consistently equal to 1/20th of a ml. You can even find inexpensive disposable pipettes, so you're not faced with the interesting problem of trying to clean them for re-use. At any rate, whichever method you use to measure drops, the best thing is to be consistent.
Q: So if a drop has many meanings, what does that mean when I'm calculating dilution percentages???
It means the nearly-universal convention for calculating dilution percentages is not a precision formula: 5 drops of EO per 5 mls (one teaspoon) of carrier is not really a 5% dilution, since 5 mls of carrier isn't really 100 of most people's drops. But don't worry! It wouldn't really be 5% even if 5 ml were 100 drops, because 5 isn't 5% of 105.
If you're creating a blend in small quantities just for your own use, these inaccuracies are truly too insignificant to fret about. As we said earlier: The conventional rules of thumb for dilution percentages are easy to remember and to calculate - so they reduce stress, and are therefore healthier for you than absolute precision, we promise!
Q: How many mls are really in an ounce?
Sherill says: It depends. And it's well worth asking each individual supplier what s/he means by his/her ounces - either that, or dealing only with suppliers who sell in mls, so you know how many you're getting!
Ounces are confusing in several ways at once. First of all, some dealers mean ounces by weight - some mean fluid ounces - I've even run into one who doesn't know whether her ounces are weighed or measured. Since most eo's are fluids at room temperature, most retail suppliers tend to use fluid ounces - but if it isn't clear from the catalog which they mean, you should ask.
If it's fluid ounces they mean ... you still have to ask how many ml they consist of. Get this: British fluid ounces and American fluid ounces are not the same! A British fluid ounce is 28.412 ml, an American fluid ounce is 29.573 ml, and which any given supplier has in mind, and/or how s/he rounds out these pesky numbers into something easier to calculate is very individual. Don't count on American suppliers using American ounces: I know some whose ounces measure out to 28 ml - some to 30 ml - and one who has some weird system whereby the number of mls per ounce wavers depending on how many ounces you're buying.
Are you ready to go metric yet? A ml is a ml no matter where you find it ...
Q: What is a dram, and why?
Gary says: If someone throws drams (fluidrams, that is) at you:
1 dram = 3.696 ml or functionally about 1/8 oz
Ask them if they're talking about fluidrams, first, though, and explain to them that aromatherapy measures are in the realm of volume, not weight, and that ought to make them go away.
If they persist, tell them that most units of what people consider as weight are really units of mass and need a gravitational field to be weight, which is really a kind of force. That ought to really make them go away dazed and confused ...
Q: Are things any clearer when a supplier sells eo's by weight?
Sherill says: Not really - but for different reasons. Selling eo's by weight isn't uncommon when you get into the large bulk arena. And by weight, the number of mls per kilo (or pound) varies with the specific gravity of the eo. Since most eo's are lighter than water, a kilo contains more than 1000 ml, but how much more than 1000 varies from oil to oil.
Naturally, the same applies when you try to translate pounds and avoirdupois ounces into mls - how many are in there depends on the specific gravity of the particular oil. (And as you become totally glassy-eyed: British avoirdupois measures are different from American avoirdupois measures.) (Go metric!)
Q: What was my next question ... ? Ah yes: cc's.
Yes, 1 cc = 1 ml.
Whatever method you choose to measure and dilute by - whether you use eyedroppers or pipettes; ounces, mls, or tablespoons; kitchen measures or nice graduated glassware - the thing is to develop a system that works for you intuitively.
Also remember to keep your measures clean, and record what you do.
Most of all, remember to have fun and learn.
Copyright © 1998 S. Pociecha and G. Bourbonais