Your body can only absorb so much carbohydrate per hour, and that ceiling rises with training. Use these ranges as a starting point and refine them in your long sessions.
5K–10K: keep it simple
Efforts under an hour are largely fuelled by what you ate beforehand. A caffeine gel just before the start can sharpen focus, but you do not need much in-race carb.
Half marathon: 30–60g/hr
Now in-race fuelling starts to matter. One to two gels across the race keeps blood glucose stable through the closing miles when it counts most.
Marathon: 60–90g/hr
This is where most “bonks” happen. Commit to a gel every 20–25 minutes from early on, using a dual-source carb so you can absorb more without GI distress.
Ironman & ultra: 80–120g/hr
Long, lower-intensity days let well-trained athletes go high. A Carb Only or Carb & Electrolyte drink mix lets you hit big numbers in liquid form, supplemented with gels and chews for variety.