Cooking Oil: Small Bottle vs Large vs Gallon — Which Size Is the Best Value?
Cooking oil is something every Thai kitchen uses constantly. The instinct is that bigger must be cheaper — but without calculating price per mL, you may actually be overpaying without realising it. Sometimes a mid-sized bottle on promotion beats the gallon on unit cost. Here's how to know for sure.
What Is Price per mL and Why Does It Matter?
Price per mL — or per 100 mL — is the only honest way to compare products sold in different sizes. It eliminates the distortion created by different package volumes and lets you see the true cost of what you're buying.
Examples:
500 mL bottle at ฿54 → 54 ÷ 500 = ฿0.108 per mL
1,000 mL bottle at ฿95 → 95 ÷ 1000 = ฿0.095 per mL
2,000 mL bottle at ฿175 → 175 ÷ 2000 = ฿0.0875 per mL
5,000 mL gallon at ฿395 → 395 ÷ 5000 = ฿0.079 per mL
From this calculation the gallon wins on unit cost. But does that mean you should always buy the gallon? Not necessarily — and the rest of this article explains why.
Price Comparison Table: Vegetable Oil Across All Sizes
Approximate prices from Thai supermarkets (2026):
| Size | Approx. Price | Price/mL | Price/100 mL | Saving vs 500 mL |
|---|---|---|---|---|
| 500 mL | ฿54 | ฿0.108 | ฿10.80 | — |
| 1,000 mL (1L) | ฿95 | ฿0.095 | ฿9.50 | 12% |
| 2,000 mL (2L) | ฿175 | ฿0.0875 | ฿8.75 | 19% |
| 5,000 mL (5L gallon) | ฿395 | ฿0.079 | ฿7.90 | 27% |
The 5L gallon is 27% cheaper per mL than the 500 mL bottle. That's a meaningful saving — if you can use it before it goes rancid.
Factors Beyond Unit Price
1. Shelf life after opening
Opened vegetable oil should ideally be used within 3–6 months. Once exposed to air, oil begins to oxidise — the process that causes that unpleasant rancid smell and degrades the oil's quality and nutritional value. If your household uses oil slowly, a 5L gallon may take 10+ months to finish, putting the last portion at risk of spoilage. The cost of wasted oil eliminates any unit price advantage.
2. Storage space
A 5L gallon weighs approximately 4.6 kg and occupies significant cabinet space — roughly equivalent to two large milk cartons stacked. If your kitchen or pantry is compact, the physical footprint matters beyond just the economics.
3. Upfront cash outlay
Even if the gallon delivers a lower unit cost, it requires a larger one-time payment. If your grocery budget is tight, buying a 1L bottle each week may fit your cash flow better than a ฿395 purchase, even if you pay slightly more per mL over time.
4. Ease of use
A full 5L gallon is heavy and awkward to pour — particularly for elderly users or anyone with limited grip strength. Many people who buy gallons decant them into smaller kitchen bottles for daily use, which introduces an extra step and increases the oil's air exposure every time you refill.
5. Promotions that flip the equation
This is the most important factor that most shoppers miss. When a 1L bottle runs a buy-one-get-one promotion, the effective unit cost drops dramatically — potentially beating the gallon:
→ You receive 2,000 mL for ฿95
→ Price per mL = 95 ÷ 2000 = ฿0.0475 per mL
5L gallon at regular price ฿395:
→ Price per mL = 395 ÷ 5000 = ฿0.079 per mL
1L BOGO is 40% cheaper per mL than the gallon
Never assume the gallon wins — always run the numbers when any promotion is involved.
Which Size Is Right for Which Household?
| Size | Best for | Not suitable for |
|---|---|---|
| 500 mL | Singles, light cooks, trying a new brand | Families of 3+, frequent cooking |
| 1,000 mL (1L) | Couples, cooking 3–4 times per week | Restaurants, large families |
| 2,000 mL (2L) | Families of 3–4, cooking daily | Singles, households that rarely cook |
| 5,000 mL (gallon) | Large families (5+), restaurants, frequent frying | Small households, limited storage space |
A Simple Three-Question Decision Framework
Before buying any cooking oil, ask yourself:
- How many mL do we use per month? Divide the bottle volume by your monthly usage to estimate how long it would last. If the answer is more than 4–5 months for an opened bottle, size down.
- Is any size currently on promotion? Calculate the promotional unit price before assuming the gallon is cheapest.
- Do I have the storage space and cash flow? If either is constrained, buy the size that fits your actual situation — the theoretical savings from a gallon are worthless if it doesn't work in practice.
Common Mistakes to Avoid
- Buying the gallon on instinct without calculating. Sometimes a smaller size on promotion is genuinely cheaper per mL.
- Buying the smallest size out of habit. If you cook daily, the 500 mL bottle is costing you 27% more per mL than the 2L option with no benefit in return.
- Keeping opened oil too long. Oil stored for more than 6 months after opening should be smell-checked. Rancid oil should be discarded — and that waste completely cancels any savings from buying bulk.
- Ignoring the weight factor. If heavy containers are difficult to pour, factor in the inconvenience cost rather than just the money cost.
Let DealCheck Do the Math
No need to calculate unit prices in your head at the supermarket. Enter the price and volume for each size and DealCheck instantly shows which is the best value — including factoring in promotions.
Open DealCheck