New Year, Better Diving: Mastering Basic Gas Planning

Of all the New Year's resolutions divers make, "get better at gas planning" is one of the most useful and one of the most quietly ignored. It's not glamorous compared to a new certification or an exotic trip, but genuinely understanding your gas consumption and planning around it properly is one of the biggest single upgrades you can make to your safety margin and your enjoyment underwater. If 2025 is the year you want to dive smarter rather than just more, this is a good place to start.

Why Gas Planning Actually Matters

Running low on air underwater is one of the most common contributing factors in diving incidents, and it's almost always preventable with basic planning done properly before you ever leave the surface. Gas planning isn't just about avoiding an emergency, though, it's also what lets you dive with genuine confidence rather than repeatedly glancing at your pressure gauge with a nagging sense of uncertainty about whether you'll have enough to get back to the boat or shore comfortably.

Good gas planning also makes you a better buddy. Knowing your own consumption rate, and having a rough sense of your buddy's, means you can plan dives that actually match both divers' needs rather than one person quietly stressing while the other cruises along unaware. It's a skill that pays off on every single dive you ever do, not just the deep or demanding ones.

The Rule of Thirds, Properly Explained

The classic starting point is the rule of thirds: a third of your gas to get out, a third to get back, and a third held in reserve for contingencies. It's most commonly associated with cave and overhead-environment diving, but the underlying logic, always keeping a genuine safety margin rather than planning to use every last bar, applies to open water recreational diving too, even if the exact split varies.

For a straightforward open water dive, many instructors teach a simplified version: plan to surface with a meaningful reserve, commonly at least 50 bar, though your agency and local conditions may specify differently, and never treat that reserve as "extra" gas to use if the dive is going well. Reserve gas exists precisely for the dive that doesn't go as planned, a stronger current than expected, a longer surface swim, or helping out a buddy who's used more gas than anticipated.

Common Mistakes Divers Make

The single most common mistake is not actually calculating a plan at all, just diving until the gauge hits a number that feels vaguely uncomfortable and heading up. That works fine until, one day, it doesn't. A close second is planning based on someone else's consumption rate rather than your own, gas consumption varies hugely between divers based on fitness, experience, body size and how relaxed you are underwater, so borrowing a buddy's numbers can leave you with a plan that doesn't actually fit you.

Another frequent error is failing to account for depth properly. Gas consumption increases with depth because you're breathing denser air, so a plan that works comfortably at 12 metres can fall apart much faster at 25 metres if you haven't adjusted your numbers accordingly. Finally, plenty of divers calculate a plan correctly and then quietly abandon it mid-dive when something interesting appears, a shipwreck, an unexpected reef shark, that discipline to stick to the plan is just as important as making it in the first place.

How to Practise and Build the Habit

Start by working out your own surface air consumption rate on a few ordinary dives, tracking your starting pressure, ending pressure, dive time and average depth. Over a handful of dives you'll get a genuinely useful personal baseline, which is far more accurate than any generic figure you'll find online. From there, practise doing a proper gas plan before every dive, even easy, familiar ones, until it becomes second nature rather than an extra chore.

It's also worth deliberately practising monitoring your gas more actively underwater rather than just glancing at it occasionally, checking in at set intervals or set points in the dive plan, so you're never caught off guard by how much you've used. Courses like Advanced Open Water and Rescue Diver both build in real gas management practice, and for divers who want to go deeper into it properly, our course listings include options specifically focused on dive planning and gas management as a dedicated skill set.

Computers, Tables and Planning Together

Modern dive computers make real-time gas monitoring far easier than it used to be, many now calculate estimated time remaining based on your current consumption rate and depth. That's a genuinely useful tool, but it works best as a cross-check against a plan you've already worked out, not as a replacement for planning in the first place. A computer can tell you what's happening right now, it can't tell you whether the plan you started with was sound.

Divers trained on tables sometimes assume computers make that background knowledge redundant, but the opposite is usually true. Understanding the reasoning behind gas planning, why depth affects consumption, why reserves matter, why plans need buddy input, makes you a sharper diver with a computer strapped to your wrist, not a less capable one. It's a foundation worth learning properly regardless of which tool you dive with day to day.

Questions We Often Get Asked

How much reserve gas is actually enough?

It depends on the dive, but a good general habit for open water recreational diving is planning to be back at the surface, or at your safety stop, with a meaningful cushion left in the tank, commonly at least 50 bar, adjusted upward for deeper, more demanding, or less familiar dives.

What if my buddy uses gas much faster than me?

Plan around the diver with the higher consumption rate, not the average. It's a basic courtesy that keeps both divers comfortable and avoids anyone feeling rushed or short-changed on bottom time because their buddy happened to be a slower breather that day.

What Instructors Actually Look For

When we're assessing gas management during training, we're not just watching the number on your gauge, we're watching whether you're checking it proactively, whether your plan matches the dive you're actually doing, and whether you communicate your gas status clearly to your buddy without being prompted. A diver who surfaces with exactly the reserve they planned for, having checked in calmly throughout, demonstrates far more genuine competence than one who happens to surface fine but couldn't have told you their plan beforehand.

We also look for good decision-making when a plan needs to change mid-dive, a diver who notices they're using gas faster than expected and adjusts the dive accordingly, turning back earlier or aborting a planned deeper section, is showing exactly the judgement that keeps divers safe for decades of diving rather than just through their training dives.

Make It Your 2025 Habit

Gas planning isn't a one-off lesson you learn once and file away, it's a habit worth deliberately rebuilding and sharpening every year, especially after a winter break when skills can feel a little rusty. Committing to genuinely planning every dive, rather than just the ones that feel obviously demanding, is a small change that pays off across your entire diving life.

If you want to properly refresh or build out these skills with proper guidance rather than working it out alone, it's exactly the kind of thing our instructors love talking through, whether that's during a refresher session or as part of a full course.

Ready to sharpen your dive planning for 2025? Browse our full course listing or get in touch for advice on the right next step - we're at Bellman Court, Great Knollys Street, Reading, or call +44 (0) 118 9761 729.