Updated 10 August 2026. Originally published April 2025.
Overnight oats are healthy, endlessly customisable, and take less than five minutes to prep. But here is the part nobody talks about: the jar itself makes all the difference.
A great jar speeds up your prep, stops leaks in your bag or fridge, and makes breakfast genuinely nicer to eat. A bad one puts people off overnight oats altogether.
This guide covers what actually matters when choosing an overnight oats jar: the right size, glass vs plastic, the six most common jar types, and the one feature most brands get wrong: the lid.
What Size Jar Should You Use for Overnight Oats?
For one standard serving of overnight oats (50g of oats with 100 to 150ml of milk), a 350ml wide-mouth jar is the ideal size. It holds the oats, the milk and a layer of toppings, with just enough headroom to stir. Go smaller (250ml) for a child's portion, or larger (500ml) only if you regularly make double servings. The same sizes apply to any overnight oats container, tub or cup.
| Jar size | What fits | Best for |
|---|---|---|
| 250ml (about 8.5 fl oz) | 30 to 40g oats plus milk | Kids, light eaters, snack pots |
| 350ml (about 12 fl oz) | 50g oats, 100 to 150ml milk, plus toppings | A standard single serving (the size we use for the OATOLOGY Jar) |
| 500ml (about 17 fl oz) | 80 to 100g oats plus milk | Big appetites, double servings, parfaits |
The OATOLOGY Jar is made for this size
350ml of thick glass, a steel lid that measures exactly 50g of oats, milk markings on the jar and a leak-proof two-lid seal. Spoon included, and over 500 ratings on Amazon UK.
250ml (about 8.5 oz): Small Jar
- Ideal for kids or light eaters
- Great for simple oats and milk mixes, but cramped once you add toppings
350ml (about 12 oz): Medium Jar
- Perfect for a standard single serving
- Leaves space for fruit, yoghurt, nut butters or protein
- This is the size used in the OATOLOGY Jar
500ml (about 17 oz): Large Jar
- Good for big appetites or double servings
- Bulkier, and takes up more fridge space
Tip: the ratio matters more than the jar. A typical serving is 50g of rolled oats (about half a cup) with 100 to 150ml of milk. For exact measurements in grams, ml and cups, see our overnight oats ratio guide.
What Size Mason Jar for Overnight Oats?
A wide-mouth pint mason jar (16 oz, about 473ml) is the best mason jar size for overnight oats. It takes a full 50g serving with toppings and leaves room to stir, though with more headroom than you strictly need. A half-pint (8 oz, about 237ml) is too small once the toppings go on, and a quart (32 oz, about 946ml) swallows a single serving whole.
| Mason jar size | Capacity | Verdict for overnight oats |
|---|---|---|
| Half-pint (8 oz) | about 237ml | Too small once you add toppings |
| Regular-mouth pint (16 oz) | about 473ml | Works, but the narrow neck makes eating and cleaning awkward |
| Wide-mouth pint (16 oz) | about 473ml | The best mason option: easy to fill, eat from and wash |
| Quart (32 oz) | about 946ml | Too big for one serving; fine for batch-mixing 3 to 4 servings to portion out |
If mason jar sizes feel like a compromise for overnight oats, that is because they are. Mason sizes were set for canning and preserving, not breakfast, so none of them quite matches a 50g single serving, and they carry no measuring marks, which puts you back on the scales every evening. That gap is exactly why the 350ml OATOLOGY Jar exists: a container sized to one serving, with a 50g measuring lid and milk markings built in.
Glass vs Plastic: Which Material Is Best for Overnight Oats?
The material is not just about looks. It affects taste, cleaning and how long the jar lasts.
Glass jars:
- BPA-free, non-toxic and food safe
- Do not absorb flavours or odours
- Dishwasher-safe and long-lasting
- Recyclable, and look better on your shelf
Plastic containers:
- Lightweight, but some plastics can leach chemicals over time
- Prone to staining and odour build-up
- Can degrade, crack or warp with daily use
That is why we chose thick, leak-proof glass for the OATOLOGY Jar: cleaner, safer, and built to last.
Must-Have Features in an Overnight Oats Jar
A good jar does not just hold your oats. It makes your mornings easier, your food fresher and your routine smoother. Here is what actually matters:
A Lid That Works (and Stays That Way)
This is the most important part, and the one most brands get wrong. A poor lid means leaks, messes and frustration. A great lid means:
- A tight, reliable seal, no guessing or double-checking
- Easy to screw on and off
- No drips in your bag or fridge
- Durable materials, not thin plastic
At OATOLOGY we spent as much time designing the lid as the jar itself, because your whole morning depends on it.
Durable, High-Quality Glass
Look for thick, break-resistant glass that stays clean and neutral (no smells or stains) and feels solid in your hand. Thin glass jars rarely survive a year of daily use.
A Jar That Fits Your Routine
A wide mouth makes filling, eating and cleaning simple. Built-in measurement guides mean perfect portions without scales or guesswork. When a jar is designed properly it becomes part of your routine instead of getting in the way.
Types of Jars for Overnight Oats (With Pros and Cons)
From classic mason jars to plastic pots, here are the most common overnight oats jars people use, and how they compare:
Classic jars / mason jars
- Pro: affordable and durable
- Con: narrow mouths and fiddly two-part lids
Clamp-top jars (Kilner style)
- Pro: airtight seal
- Con: bulky, and awkward to eat from
Minimalist pantry jars
- Pro: stylish and modern
- Con: often no proper seal, and no spoon
Yoghurt-to-go cups
- Pro: lightweight with a built-in spoon
- Con: usually plastic, and prone to leaking
Mason jars with a spoon clip
- Pro: handy for commuters
- Con: the spoon often gets lost or dirty
Bamboo-top jars
- Pro: cheap
- Con: thin glass, and not built for carrying
Pro tip: the best all-rounder is a 350ml wide-mouth glass jar with a secure lid and a spoon, which is exactly what the OATOLOGY Jar is. For a comparison of specific jars you can buy in the UK, see our best jars for overnight oats UK round-up.
Why We Designed the OATOLOGY Jar the Way We Did
We tested dozens of jars. None had everything we wanted, so we made one that did. Every feature of the OATOLOGY Jar solves a real problem:
- The portion system is built in. The stainless steel lid measures exactly 50g of oats, and milk markings on the back of the jar show exactly where to fill. No scales, no guesswork, one perfect portion every time
- Two-lid leak-proof seal. The steel measuring lid screws down over a silicone sealing lid, so it survives a commute in your bag
- The right size. 350ml, sized for one full serving of oats, milk and toppings, with a genuinely wide mouth for easy filling, eating and cleaning
- Thick, break-resistant glass with the OATOLOGY logo embossed on the front
- A complete kit. Stainless steel spoon included, with a silicone holder that clips it to the jar for breakfasts at your desk
- Dishwasher-safe glass body. Give the steel lid a quick hand wash to keep it looking new
If overnight oats are part of your routine, or you want them to be, this jar makes the whole thing easier and tidier.
Frequently Asked Questions About Overnight Oats Jars
What size jar is best for overnight oats?
A 350ml (about 12 fl oz) wide-mouth jar is best for a single serving of overnight oats: 50g of oats, 100 to 150ml of milk and room for toppings. If you use mason jars, a wide-mouth pint (16 oz, about 473ml) is the closest fit. The same numbers apply to any overnight oats container: aim for 350 to 500ml.
Can I use any jar for overnight oats?
Yes. Any clean jar with a lid will make overnight oats. For everyday use, though, a wide-mouth, leak-proof glass jar is worth it: easier to fill, easier to eat from, easier to clean, and no surprises in your bag.
Do overnight oats need a lid?
Yes, always cover overnight oats in the fridge. A lid stops the oats drying out and absorbing fridge smells, and you need a proper seal if you carry breakfast to work. For how many days they keep, see our guide to how long overnight oats last.
Can I make overnight oats in a plastic container?
You can, and for occasional use it is fine. For regular use glass wins: it does not stain, hold odours or degrade, and it keeps your oats tasting the way they should.
How do I clean an overnight oats jar?
Rinse it soon after eating, then wash in warm soapy water, or in the dishwasher if it is a wide-mouth glass jar. The OATOLOGY Jar's glass body is dishwasher safe; hand-wash the steel lid. One thing to avoid: the microwave. Most storage jars, ours included, are not microwave safe.
Is a spoon really necessary?
If you eat breakfast at your desk, at the gym or on the go, yes. Arriving with oats and no spoon gets old fast, which is why the OATOLOGY Jar includes a steel spoon with a clip-on holder.
Recipes Made for This Jar
Every recipe in the OATOLOGY Kitchen is written for a 350ml jar: 50g of rolled oats, 150ml of milk and 1 tbsp of chia seeds, measured in grams and ml with cup equivalents. Pick one tonight and it is ready by morning.
- Peanut butter and banana overnight oats: nutty, creamy, the one to start with
- Mango and coconut overnight oats: coconut milk and fresh mango, naturally vegan
- Blueberry and lemon overnight oats: Greek yoghurt and lemon zest, sharp and fresh
- Chocolate and raspberry overnight oats: cacao and raspberries, pudding for breakfast
- Strawberry cheesecake overnight oats: cream cheese base, crushed biscuit on top
- Apple pie overnight oats: stewed cinnamon apple, layered
- Blended berry overnight oats: blended smooth with berries, no lumps
- Banana bread overnight oats: ripe banana, cinnamon and a caramelised banana topping
All eight, with the guides below, live at recipes.oatologystore.com.
More from the OATOLOGY Kitchen
- The overnight oats ratio, in grams and ml
- How long do overnight oats last?
- 8 overnight oats recipes made for the jar
Final Thoughts: A Better Jar = A Better Breakfast
Overnight oats are already easy. The right jar makes them effortless. If you want to save time, eat better and simplify your mornings, a jar built specifically for overnight oats is the upgrade you did not know you needed.
Shop the OATOLOGY Jar with free UK delivery, or buy it on Amazon UK with Prime delivery. Premium glass, perfect portions, no leaks, no stress.