How Many Calories Are in a Gin and Diet Tonic Water? All You Need To Know

Do you fancy a G&T but aren’t sure how many calories are in it? You aren’t alone. If you’re curious about watching your calories or just curious about what’s in your glass, this article is for you.

Many people are curious to know if you can really tell the difference between switching out plain tonic for diet tonic. Spoiler alert: it does. But the devil is in the details. Let us tell you what you’d want to know before you head to the pub or try making one yourself.

The Basics: What’s in a Gin and Tonic?

A classic gin and tonic is not complicated. It’s just gin, tonic water, and perhaps a few cubes of ice and a wedge of lime.

Gin is a clear, distilled alcoholic drink that is considered the very essence of spring and summer. Tonic water is a bubbly mixer that mitigates gin’s robust flavour. Gin has about 37.5% to 40% alcohol by volume.

There is sugar in regular tonic water. Diet tonic uses sweeteners and is thus lower in calories. That switch is the biggest difference (if you’re trying to keep track of your daily intake).

Calories in Gin

Let’s start with the gin itself.

A single measure of gin in the UK (that’s 25ml) has about 54–60 calories.

If you’re having a double measure (50ml), you’re looking at 108–120 calories.

The calorie count doesn’t really change between brands. Whether you’re drinking a big name like Gordon’s or a fancy craft gin, the alcohol is the bit with calories.

Calories in Tonic Water

Regular tonic water is where it can sneak up on you.

A 150ml serving (about what you’d get in a pub or at home with a standard pour) has roughly 50–60 calories. That’s basically the same as adding a biscuit to your drink.

Not terrible, but if you’re having a few, it adds up quickly.

Diet tonic water, though? Almost nothing.

Most UK diet tonic brands have 1–2 calories per 150ml serving. Some even say “zero calories” on the label. It’s sweetened with artificial or plant-based sweeteners instead of sugar.

So How Many Calories are in a Gin and Diet Tonic?

Right, let’s do the maths in a way that actually makes sense.

• Single gin (25ml) + diet tonic (150ml): about 55–60 calories total

• Double gin (50ml) + diet tonic (150ml): around 110–120 calories

That’s it. The diet tonic barely adds anything. If you swapped in regular tonic for diet tonic, you’d be adding around 50–60 extra calories per drink.

So your single G&T with regular tonic would be roughly 105–120 calories. Your double could hit 170–180 calories or more.

Why Do People Choose Diet Tonic?

The biggest reason is pretty clear—it cuts the calories almost in half.

For anyone watching their daily intake or trying not to go overboard on “liquid calories,” diet tonic is a really easy switch. You’re still getting the same gin taste, just with fewer sugary calories.

Some people also prefer the taste. It’s often less sweet and lets the botanicals in the gin stand out more. Others don’t love it at all—it’s a bit of a Marmite situation.

A Quick Look at Other Popular Mixers

Just for context, here’s how other widely known mixers stack up:

• Cola (150ml): around 60–65 calories
• Diet cola (150ml): 1–2 calories
• Orange juice (150ml): around 65-70 cals
• Slimline tonic: generally 1–2 calories

So, diet tonic is one of the lowest-calorie mixers you can use.

Does the Garnish Add Calories?

Not really. A slice of lime or lemon could be a calorie or two. You have nothing to worry about. If you make fancier garnishes—cucumber ribbons, herbs, berries—the calorie effect is still minuscule. The gin and the mixer are what really count, after all.

Watch Out for Flavoured Gins

One thing to keep in mind: not all gin is the same.

Some of the new flavoured gins on the market have added sugars or sweeteners. That can bump up the calorie count.

If you’re picking a pink gin or something with a flavour twist, check the bottle. Some are just as light as regular gin, others are closer to a liqueur and have extra calories.

Drinking at Home vs the Pub

Measurements matter.

• At home, you might pour a 25ml single (if you use a jigger) or a 50ml double. But let’s be honest—lots of us free-pour and go a bit heavy. That adds up quickly.
• In pubs, single or double is usually clearly marked, so it’s easier to track.

If you’re watching your calories, measuring your pour is a smart move.

Final Thoughts

So, how many calories are in a gin and diet tonic water?

• A single contains about 55–60 calories.
• Double has about 110 to 120 calories.

That’s it. A simple switch to diet tonic can save you several hundred calories over the course of a night.

Of course, it’s not all about calories. If you like a real gin and tonic with full-sugar tonic, have at it. Just know what you are drinking.

And, at the end of the day, it’s all about balance. Do the drinks you like, know what’s in them, and do what feels right for you.

So the next time you’re out or making one at home, you’ll have a sense of what you’re drinking. Cheers!