How To Read A Supplement Label – Units, Symbols, & What They Really Mean

Do you find supplement labels confusing? Are you baffled by the different measurements for vitamins and minerals?  Not sure what RNI, DRV, and RDA really mean? 

It’s a minefield, we know. So, we’ve put together this handy guide on how to read a supplement label to get you up to speed on the label lingo.

Start with the ingredients 

First, look at the ingredients list. Here you can check out the form of each vitamin and mineral. For example, does your calcium supplement contain highly bioavailable calcium citrate, or poorly absorbed calcium carbonate? It’s worth reading so you know what you’re taking.

You’ll also see everything that isn’t an active ingredient – i.e. any binders, fillers, or other synthetic additives. Here at Ethical Nutrition we don’t use any synthetic ingredients in our products. The only thing you’ll find listed beside the active ingredient is a tiny amount of organic, gluten-free rice concentrate – or nothing at all.

Next, look at how much of the active ingredient is in the product. Vitamins, minerals, herbs, and other nutrients are measured in grams, milligrams, or micrograms. Some vitamins and minerals are also shown as a percentage of your Nutrient Reference Value or NRV.

What’s the difference between RDA, NRV, and RNI?

NRV, RDA, RNI – what do they all mean?

• Recommended Dietary Allowance (RDA): RDA levels were first established in 1943 by the US Food and Nutrition Board. They were judged to be the amount of essential vitamins and minerals healthy people need to get from their food [1].

• Nutrient Reference Values (NRV) are a newer form of measurement that has largely replaced the RDAs in the UK and Europe. NRVs are set for 13 vitamins and 14 minerals. They’re guidelines about the amount of vitamins and minerals that should be consumed on a daily basis to maintain a healthy adult [2].
  
  For example, a vitamin C label may say “vitamin C 80mg / 100% NRV” because 80mg is the amount a healthy adult requires to prevent deficiency. Different countries use different criteria to establish NRVs which is why the amounts can vary.

• Reference Nutrient Intake (RNI) levels are part of a set of Dietary Reference Values (DRVs) that also include Estimated Average Requirements (EARs), Lower Reference Nutrient Intake (LRNI), and Safe Intake (SI) levels.
  DRVs estimate the energy and nutrient requirements of different groups of healthy people in the UK population. There are separate DRVs for males and females, children, adults, older people, and for pregnancy and breastfeeding. RNIs are an estimate of the amount of each vitamin and mineral that is likely to prevent deficiency in 97.5% of each category.

An important point about RDAs, NRVs, and RNIs is that they’re based on keeping already healthy people, healthy. However, people use supplements to make up for gaps in their diet, address deficiencies, and meet individual increased needs for specific nutrients. This is why many supplements provide levels of nutrients that go above and beyond the NRV and RNI.

Micrograms vs Milligrams

It’s easy to get these two measurements mixed up (it’s all the M’s and G’s) but there’s a significant difference between them.

A microgram is 1000th of a milligram: 1000mcg = 1mg.

A milligram is 1000th of a gram – 1000mg = 1g.

Mcg, µg, ug… What’s the Difference?

Just to make matters even more confusing, there are 3 different symbols for microgram.

The official symbol used in the International System of Units [3] is the Greek letter  “µ”. You may also see it written as “mcg” or, less commonly, “ug”. They all mean the same thing – microgram.

What are International Units?

International Units (“IU” or “iu”) represents the activity or potency of a vitamin, rather than its weight. It is the amount of a substance that has a biological effect. You will most commonly see it as a measurement for vitamins A, E, and D.  Sometimes the iu is listed alongside the weight, for example 25µg/1000iu of vitamin D. 

FAQs

What is the difference between mcg and µg?

There is no difference between mcg and µg. Both represent how much something weighs in micrograms.

How many micrograms are in a milligram?

There are 1000 micrograms in a milligram.

What does NRV mean on a supplement label?

NRV stands for Nutrient Reference Value. There are NRVs given for 13 vitamins and 14 minerals, and these have largely replaced RDAs (Recommended Dietary Allowance) in the UK and Europe. An NRV is the amount of a vitamin or mineral that a healthy adult needs to consume every day to maintain their health.

Is mcg the same as ug?

Yes, mcg, ug, and µg all stand for microgram.

How do I know if a supplement dose is too high?

We strongly advise you to follow the recommended dosages for each supplement. Our dosage guidance is based upon the safe upper levels for vitamins and minerals guidance issued by the Expert Group on Vitamins and Minerals [4], so you can be confident that the recommendations are safe for your health.

Remember that it’s important to consult your GP or healthcare practitioner before taking supplements alongside prescription medications to ensure there are no contraindications.

What does 200µg mean in mg?

In milligrams, 200µg equates to 0.2mg.  

One milligram is the same as 1000 micrograms.

We hope this guide helps you better understand the often-confusing world of supplement labels. Get in touch if you have any questions and remember to take our free quiz to find the right supplements and meal plan for you – all in less than one minute!

You may also enjoy reading:

How to boost Magnesium Absorption

Best Vitamins for Vegans

8 Ingredients to Avoid In Your Supplements

The Evidence

1. National Research Council, 1989. (US) Subcommittee on the Tenth Edition of the Recommended Dietary Allowances. Recommended Dietary Allowances: 10th Ed. Washington (DC): National Academies Press (US); 1989. 2, Definition and Applications. Available from: https://www.ncbi.nlm.nih.gov/books/NBK234926/ [Accessed 15 Aug 2025].

2. Department of Health, 2017. Technical guidance on nutrition labelling. [online] Available at https://assets.publishing.service.gov.uk/media/5a8010d8e5274a2e87db7a62/Nutrition_Technical_Guidance.pdf [Accessed 15 Aug 2025].

3. Britannica, n.d. International System of Units. [online] Available at https://www.britannica.com/science/International-System-of-Units [Accessed 15 Aug 2025].

4. Department of Health and Social Care, 2024. Nutrition Legislation Information Sheet [online] Available at https://www.gov.uk/government/publications/nutrition-legislation-information-sources/nutrition-legislation-information-sheet--2#food-supplements [Accessed 18 Aug 2025].