If you haven’t read How to Minimize GI Distress When Running (By Mixing Your Own Sports Drink), do that first. It provides the context you’ll need to get the most out of this calculator.
Disclaimer: This calculator requires the use of the ingredients below. Adding other ingredients will lead to an inaccurate tonicity calculation.
Outside the United States? If Amazon in your country doesn’t have the same product, search for equivalents using these terms: maltodextrin powder, fructose powder, sodium citrate, or citric acid.
For the best experience, view the calculator on a computer and not a mobile device.
Step 1: Figure Out Your Desired Nutrition Per Hour
In the calculator above, change the orange numbers next to each ingredient with how much nutrition you want per hour.
I recommend starting with how much you’re currently getting per hour from traditional sports drinks or gels. That way you’re starting from something you know works with your gut.
If you’re outside the United States, make sure to change the drop down from
US fluid oz to
imperial fluid oz.
Fructose serves double duty as a source of carbs and a sweetener. You should add just enough fructose to get your preferred sweetness.
Once you have the desired sweetness from fructose, subtract the amount of fructose from the total amount of carbs you want per hour to figure out how many carbs you’ll need from maltodextrin.
For example, if you want 25g of carbs per hour and are using 8g of fructose, enter 17g for maltodextrin.
How much sodium you’ll need is a little more subjective.
350mg is a good starting point.
But if you’re a salty sweater (i.e. salt crystals form on your skin or your sweat tastes salty) then you might want to try 500-1000mg per hour depending on the sodium concentration of your sweat.
This is a non-essential (read: optional) ingredient but does add a bit of flavoring that makes the drink taste a bit better (and less like sugar water).
It’s up to you to figure out how many packets you want in your mix.
Step 2: Enter the DE of Maltodextrin
Maltodextrin is classified by its dextrose equivalent (DE) that ranges from 3 to 20. All maltodextrin I’ve seen sold for food purposes has a DE of 10, so it’s safe to assume that number here.
However, if you’re using maltodextrin with a different DE, enter that number here as it affects tonicity.
Step 3: Review Tonicity
Once you’ve specified how much nutrition you want per hour, look at the blue strip that shows osmolarity and tonicity.
Make sure the tonicity matches what you want out of your sports drink.
- Isotonic (recommended): Hydration and nutrition
- Hypotonic: Hydration over nutrition
- Hypertonic: Nutrition over hydration
If you want a better understanding of the pros and cons of each, read this primer on tonicity.
When adjusting the ingredient ratios, keep in mind maltodextrin impacts tonicity the least while fructose and sodium impacts it the most.
Step 4: Mix the Drink
Look under the Serving Size column to see how much of each ingredient to mix together.
If you need a kitchen scale (super handy), here’s a well-reviewed one.
Pro tip: Put an empty bottle on the scale and hit the Tare button. That resets the weight to zero (including the bottle). Then keep hitting the Tare button after each ingredient. That makes it really easy to add ingredients one after the other without having to take the drink off the scale.
I’m sure that’s a common feature of all scales but it blew my mind. This is why it pays to read the instruction manual. ?
Step 5: Keep a Journal
As you’re going down this rabbit hole of trying different recipes, it’s worth keeping a journal. Make note of how much you’re using of each ingredient and how your body responds. Do you feel full or bloated? Are you experiencing cramps or GI distress?
You should treat it like a science experiment and only change one thing in the recipe at a time (e.g. the amount of fructose or sodium). If you change multiple things at a time and your body reacts poorly, you don’t know which change resulted in the reaction.
Over time, a journal will give you insight into what your body can and can’t tolerate.
Also know you can train your body to tolerate more carbs per hour. So if you need more carbs, find the current amount you can tolerate per hour and gradually increase it over time.
Let me know in the comments if you have any questions!
14 replies on “DIY Sports Drink Tonicity Calculator”
Hi Alex, this is fantastic, thank you so much for sharing your work!
How do you think companies like Maurten are ensuring their 320 Drink Mix stays isotonic? It’s recommended to be mixed with 500ml/17foz of water, and provides 320 calories, 80g carbs and 500mg salt?
Seems imposisble with your calculator, what wizardry do they have?!
Are you sure the DE value is used in your calculator correct way? Based on my understanding maltodextrin with DE 6 has less monomeric sugars than in DE 10. This means that there is more molecules/g in DE 10 than in DE 6 which is leading to higher molality in solution in case of DE 10 if same weight is added. However, calculator is calculating higher tonicity for DE6 than DE10? How the molality in case of maltodextrin is calculated, and how the DE is used in the calculation?
I found an article where we can find good basic knowledge about the topic: Castro, N., et al., “Influence of DE-value on the physicochemical propertie4s of maltodextrin for for melt extrusion processes”. The topic of the research is not so interesting in this content but there good background for these relevant calculations. Based on these I’ll calculated molar mass for DE 10 to be 1818 g/mol (yours 1639) and 3018 g/mol for DE 6. In your calculator the molar mass for DE 6 is 990.9 g/mol. So this is causing wrong calculations.
i’ll need to dive in a bit more when i have some time, but i thought i had fixed the calculations based on this comment:
unless i’m misinterpreting, my understanding is that the variable n in the page linked to in the above comment is the DE value. so if n = 10, that means the molar mass calculation is for DE10.
the calculator currently spits out the correct values based on that assumption.
but i admit, i could be very wrong in that assumption because asking chatGPT gave me a different value (which is also different from your calculations):
what’s the molar mass of maltodextrin with a DE of 10?
To calculate the molar mass of maltodextrin with a DE of 10, we need to first calculate its degree of polymerization (DP) using the equation:
DP = 1 / (1 – DE/100)
Substituting DE = 10 into the equation, we get:
DP = 1 / (1 – 10/100) = 1.11
Now, we can calculate the molar mass of maltodextrin using the formula:
Molar mass of maltodextrin = DP x molar mass of glucose
Substituting DP = 1.11 and the molar mass of glucose (180.16 g/mol) into the equation, we get:
Molar mass of maltodextrin = 1.11 x 180.16 g/mol = 200.0 g/mol
Therefore, the molar mass of maltodextrin with a DE of 10 is approximately 200.0 g/mol.
Why do you have the molar mass of the maltodetrin linked to that of the fructose?
great question, and i don’t know. 😅
but, i’ve fixed it now so the molar mass should be accurate based on what’s found here:
for example, if you change the DE to 3, you should see the molar mass updated to 504.5.
thanks for pointing it out! the good news is that the osmolarity value was only off by a few (e.g 264 versus 261) with the old molar mass. so not anything that would’ve noticeably affected peoples’ results.
How is the sodium per hour calculated in the serving size column? If I input 400mg sodium it shows a serving of 1.7g. I’m using sodium citrate powder.
i’m basically following the nutrition facts on the label for sodium citrate. it says 3g of sodium citrate is 700mg of sodium. so if you want 400mg of sodium in your mix, you would need to use 1.7g of sodium citrate.
Hi Alex, do you have any information on using cyclic dextrin over maltodextrin?
unfortunately not. i haven’t heard of that before.
Thanks for the tonicity calculator very helpful but I do have a question on it. I was of the understanding that one of the reasons sports drinks use maltodextrin e.g. “MDE10” is to reduce the tonicity by using larger longer chain glucose molecules. When I was trying to compare the tonicity of a MDE10 mix verses a sugar mix I ended up with higher tonicity for the MDE10 which seems counter intuitive? The way I replicated sugar in you calculator was to have fructose and MDEX 50:50 and set the DE value for MDEX to 1 which should be correct for glucose? Let me know if I have missed something? Super interesting topic by the way 😉
yikes, i’m not entirely sure my calculator is suited to calculating the tonicity of a sugar mix. it was tailor made for the exact ingredients i listed. i think your question is above my pay grade. 😅
Hello have are you geat calculator. I have a question. I dont know the DE of the maltodextrin im using i know you put 10 in the calendar but went i use the number 10 give me a different osmolality if i use 15 or 20. How many oz of water do i need to get 90g of carbs per hour to be isotonic.
if you don’t know the DE then i would just assume 10. based on what i’ve seen, that seems to be the norm for maltodextrin in sports drinks. to answer your question, use the calculator and play around with different values until it tells you the drink mix is isotonic.