Ethan BrooksBy Ethan Brooks

Energy gels with 40g carbohydrates are one of the most common fueling tools for marathoners and half marathoners. This guide explains what a 40g serving means in practice, how to decide how many to take, when to take them, and how to test them in training before race day. By the end, you will have a simple plan you can adapt to your own pace, body and race distance.

What 40g of Carbohydrates Means in an Energy Gel

Most energy gels are sold as single-serving packets, and the label usually lists carbohydrate content per packet. A 40g carbohydrate gel delivers roughly 160 calories from carbohydrates alone, since carbohydrates provide about 4 calories per gram. Some gels contain a small amount of fat or protein, so the total calorie count may be slightly higher, but the carbohydrate figure is what matters most for fueling.

Shopping for one? See our guide: Honey Stinger Energy Gels: 8 Best Options for Marathon Fueling (2026).

Forty grams is a substantial dose. For many runners it is a full hour of carbohydrate intake in a single packet, which is why timing and pacing your intake matter as much as the product itself.

Carbohydrate needs vary with body size, pace, duration and individual tolerance. Sports nutrition guidance commonly cites roughly 30 to 60 grams of carbohydrate per hour for efforts lasting longer than about 90 minutes, with higher targets sometimes used by well-trained athletes who have practiced their gut tolerance. A single 40g gel therefore covers a meaningful portion of your hourly target, and it is best thought of as a building block rather than a complete fueling plan.

How to Plan Your Gel Intake Step by Step

Use the following steps to turn a 40g gel into a realistic plan for your race or long run.

Step 1: Estimate Your Hourly Carbohydrate Target

Start with a target in the range of 30 to 60 grams per hour. Newer runners and those with sensitive stomachs usually begin at the lower end. Runners who have trained their gut over several months may work toward the higher end. Keep your number conservative until you have tested it.

Step 2: Divide Your Target Into Gel Doses

If your target is 60 grams per hour and each gel contains 40 grams, you would take one gel plus a small carbohydrate source, such as a sports drink, to reach the total. If your target is 40 grams per hour, one gel per hour is a direct match. Work out the number of gels you need for your total race time using the table below.

Race Duration Hourly Target (grams) Total Carbohydrates Needed Approximate 40g Gels
Half marathon (about 1.5 to 2 hours) 30 to 40 45 to 80 1 to 2
Marathon, 3 hours 40 to 60 120 to 180 3 to 4
Marathon, 4 hours 40 to 60 160 to 240 4 to 6
Marathon, 5 hours or more 40 to 60 200 or more 5 or more

These figures are planning estimates, not prescriptions. Your own gut tolerance and conditions such as heat should guide the final number.

Step 3: Choose Your Starting Point

Many runners take their first gel somewhere between 45 and 60 minutes into a run, then repeat at regular intervals. Some athletes start earlier in a long race. A common approach is to take the gel with a few sips of water, which helps the gel move through the stomach. Avoid taking a 40g gel right before a hard effort or a tempo segment if you have not tested that combination.

Step 4: Pair Carbohydrates With Fluid

Each gel should be followed by water, typically about 100 to 200 milliliters (roughly 3 to 7 ounces), depending on heat and sweat rate. Without enough fluid, the concentrated carbohydrate can cause stomach discomfort. In hot weather, you may need to adjust both fluid and sodium intake. A registered dietitian or sports medicine professional can help you build a personalized hydration plan, especially if you have a medical condition.

Step 5: Test Everything in Training

Never try a new gel for the first time on race day. Use your long runs to practice the exact product, the exact timing and the exact fluid you plan to use. Note any bloating, cramping or nausea, and adjust. Runners often find that taking a gel at the same interval and with the same fluid across several long runs produces the most reliable results.

Key Factors That Affect How a 40g Gel Works for You

Several variables change how your body responds to a 40g dose. Understanding them helps you adjust your plan without guesswork.

  • Pace and effort level: Higher intensity slows gastric emptying, so the same gel may feel heavier during a fast finish than during an easy long run.
  • Temperature and humidity: Heat increases fluid needs and can make concentrated gels harder to tolerate.
  • Body weight and muscle mass: Larger athletes may need more total carbohydrate across a race.
  • Gut training: Regular practice with carbohydrate intake during runs tends to improve tolerance over time.
  • Individual sensitivity: Some runners tolerate multiple gels per hour, while others do best with one.

Tips and Common Mistakes to Avoid

Common Mistakes

  • Taking gels without water: This is one of the most frequent causes of stomach upset. Always pair a gel with fluid.
  • Starting too late: Waiting until you feel depleted makes it harder to recover. Begin fueling early and keep a steady rhythm.
  • Stacking gels too closely: Taking two 40g gels back to back can overload your system. Space them out.
  • Racing with an untested product: Brand-new gels, flavors or caffeine levels can cause unexpected reactions. Test them first.
  • Ignoring expiration dates: Old gels can separate or lose texture, which affects how easily they are digested.

Practical Tips

  • Carry gels in a race belt or a pocket you can reach without stopping. Many runners prefer a belt with loops for two or three packets.
  • Tear the packet before you need it, so you are not fumbling mid-stride.
  • Label your gel plan on a card or in your watch notes, with times for each intake.
  • If your race provides gel stations, check the product and carbohydrate content in advance. Brands and serving sizes differ.
  • Use a stopwatch or watch alert set to your intake interval to avoid forgetting.

A small set of supplies can make a 40g gel plan much easier to follow on the road.

  • Running belt with gel loops: Keeps two or three packets secure and reachable without bounce. View on Amazon
  • Soft flask handheld bottle: Lets you sip water with each gel without slowing down. View on Amazon
  • Running watch with interval alerts: Reminds you when to take the next gel so timing stays consistent. View on Amazon

FAQ

Is one 40g energy gel enough for a marathon?

Usually not on its own. Most marathoners need several gels or a combination of gels, sports drink and other carbohydrate sources across the full distance. A single gel can serve as one part of the plan.

How soon before the race should I take a gel?

Many runners take a gel within about 15 to 30 minutes before the start as a pre-race top-up, but this depends on your breakfast timing and stomach tolerance. Test this in training.

Can I take a 40g gel every 20 minutes?

That would deliver about 120 grams per hour, which is well above most sports nutrition recommendations for typical runners. Only very trained athletes who have built gut tolerance usually approach such intake, and it should be practiced first.

What happens if I get stomach cramps after a gel?

Stop adding gels for a while, sip water, and avoid stacking more carbohydrate. Review your fluid intake, pacing and whether you took the gel too close to a hard effort. If symptoms are severe or recurring, consult a doctor or sports dietitian.

Should I take a 40g gel with caffeine?

Some gels contain caffeine. Caffeine can help some runners later in a race but may cause jitters, sleep issues or stomach discomfort in others. Check the label and test caffeinated products in training before using them on race day.

Do I need to take a gel if I eat a big breakfast?

Breakfast helps top up glycogen stores, but it does not replace in-race carbohydrate intake for efforts longer than about 90 minutes. Most runners still benefit from taking carbohydrate during the event.

Can I use a 40g gel for a half marathon?

Many half marathoners need only one or two gels, depending on pace and conditions. If you are running a fast half marathon, an early gel can help, but practice first so you know how your body responds.

Are gels the only option for carbohydrate intake?

No. Sports drinks, chews, bars and some real foods can also provide carbohydrate. Gels are popular because they are compact and quick to digest, but you can mix sources to meet your target.

Conclusion

An energy gel with 40g carbohydrates can be a practical and efficient part of your marathon or half marathon fueling plan. Calculate your hourly target, divide it into gel doses, and always pair intake with water. Test your exact plan in training so race day feels familiar, and consult a registered dietitian or sports medicine professional if you have a medical condition or ongoing digestive issues.

Ready to choose one?

Ethan Brooks

About Ethan Brooks

Ethan Brooks is part of our editorial team and reviews and edits our marathon & half-marathon guides, checking product details against manufacturer specifications and owner feedback.