Jigger Measurements: UK ml, US oz and Imperial oz Compared

A jigger is not one universal volume. In a UK home bar, a double-ended tool is often marked 25ml and 50ml. Other tools use 15/30ml, 30/60ml or 35/70ml. In an American recipe, 1 fluid ounce means about 29.57ml; an imperial fluid ounce is smaller at about 28.41ml. Read the engraving on the tool and the convention used by the recipe instead of treating “one jigger” as a fixed number.

This guide separates three questions that are often mixed together: the capacity printed on a home jigger, the quantities in an American cocktail recipe, and the legal measures used when certain spirits are sold by the glass on licensed UK premises. The conversion data was checked on 3 September 2026 against GOV.UK, NIST and a UK government conversion table.

Download the reusable ml/oz conversion table (CSV). Keep the checked date and source links if you reuse it.

Quick answer: common jigger markings

The table converts volume; it does not make every tool equally accurate. A decorative cup with no readable graduation is harder to repeat than a clearly engraved measure.

Full ml to fluid-ounce conversion chart

For recipe work, round sensibly. Treat 1 US fl oz as 30ml and half a US fl oz as 15ml unless the recipe requires laboratory precision. Do not switch between US and imperial fluid ounces midway through one recipe.

Why 1 oz is not always the same number of ml

The word ounce can refer to mass or fluid volume. Cocktail recipes mean a fluid ounce. NIST lists the US fluid ounce as approximately 29.57ml. The UK government conversion table lists the imperial fluid ounce as approximately 28.41ml. The difference is about 4%, which is small in one drink but becomes noticeable across a batch.

Modern cocktail books and US-origin websites usually mean US fluid ounces. Older British material may use imperial fluid ounces. If the source does not say, look at the other measures: a 2oz base spirit paired with 0.75oz citrus is probably a US-style recipe, while a modern UK venue is more likely to print millilitres.

What UK law actually says about spirit measures

GOV.UK states that gin, rum, vodka and whisky sold by the glass must be sold in either 25ml and multiples of 25ml, or 35ml and multiples of 35ml. A premises uses one of those systems, not both. The March 2026 WM 1008 bulletin also explains that measuring equipment used for trade must meet the relevant approval and marking requirements.

That rule is about selling specified spirits on licensed premises. It does not declare every cocktail jigger in Britain to be 25ml, and it does not force a home recipe to use a pub measure. Other spirits and liqueurs can fall under different quantity rules. If you operate a licensed venue, use approved equipment and current trading-standards guidance rather than treating a home-bar article as compliance advice.

How to read a double-ended jigger

1. Find the engraved capacity. Check both cups and any internal lines before pouring.
2. Keep it level. Hold the measure over the shaker or mixing glass so a spill lands in the drink, not on the worktop.
3. Fill to the intended line. A meniscus and surface tension make an overfilled dome inconsistent.
4. Pour promptly. Thick syrups and liqueurs cling to the cup; allow a short, repeatable drain rather than waiting a random length each time.
5. Use the same tool for the whole drink. Switching between an unmarked cup, tablespoon and jigger adds avoidable error.

Converting an American recipe to a 25/50ml jigger

Suppose a recipe calls for 2oz spirit, 0.75oz citrus and 0.5oz syrup. A practical metric build is 60ml spirit, 22.5ml citrus and 15ml syrup. With a 25/50ml jigger:

• Measure 50ml plus 10ml for the spirit.
• Measure 20ml plus a small 2.5ml increment for the citrus, or use 25ml and taste.
• Measure 15ml syrup using an internal line or a separate marked measure.

Do not round every ingredient in the same direction. Changing 22.5ml citrus to 25ml while also changing 15ml syrup to 20ml makes a different drink. Choose one clean metric ratio, record it, then adjust after tasting.

Can you use teaspoons and tablespoons instead?

NIST gives an approximate US teaspoon as 4.93ml and tablespoon as 14.79ml, so 5ml and 15ml are useful kitchen approximations. The weak point is the utensil: an ordinary eating teaspoon is not a calibrated measuring spoon. Use a marked cooking measure and reserve it for small ingredients such as saline, syrup or bitters batches.

For the 25–60ml volumes that form most cocktails, a graduated jigger is faster and more repeatable. The commerce panel below links to clearly marked home-bar measures; check the actual engraving and capacity before buying. Those are affiliate links where configured, at no extra cost to you.

How to check a home jigger

For a practical home check, compare the cup with a trusted graduated kitchen measure over several fills. You can also weigh room-temperature water on a reasonably accurate kitchen scale as a rough cross-check, because one millilitre of water is close to one gram under normal kitchen conditions. This is not legal verification for trade and does not replace approved equipment on licensed premises.

If a nominal 25ml cup repeatedly differs by several millilitres, use its real measured capacity in your home recipes or replace it. Consistency matters more than the shape of the tool.

Choose the right jigger for a UK home bar

• 25/50ml: convenient for UK recipe ratios and bottle unit calculations.
• 30/60ml: convenient for recipes written in 1oz and 2oz.
• 15/30ml with internal lines: useful for split bases, syrups and citrus adjustments.
• Tall Japanese-style measure: easier to fill precisely for some users, but the printed capacities still matter more than the silhouette.

Look for durable markings, several useful internal graduations and a shape you can empty cleanly. A home tool does not need to look like pub equipment, but it should state what it holds.

Sources and method

• GOV.UK — specified quantities for alcohol sold by the glass
• GOV.UK — WM 1008 measuring-equipment bulletin, March 2026
• NIST — US customary to metric conversion factors
• Northern Ireland Civil Service — imperial to metric conversion factors

Each CSV row divides millilitres by 29.5735 for US fluid ounces and by 28.41 for imperial fluid ounces, then rounds to three decimal places. The display table uses the same values. Checked 3 September 2026.

Frequently Asked Questions

How many ml are in one jigger?

There is no single universal jigger size. Common markings include 25/50ml, 30/60ml, 15/30ml and 35/70ml. Read the capacity on the actual tool.

Is a UK jigger 25ml or 35ml?

Both sizes exist. For gin, rum, vodka and whisky sold by the glass, licensed premises use either 25ml and its multiples or 35ml and its multiples. A home cocktail tool may use either or another clearly marked capacity.

Is 1oz exactly 30ml?

No. One US fluid ounce is about 29.57ml, so 30ml is the practical cocktail rounding. One imperial fluid ounce is about 28.41ml.

How many ounces are 25ml and 50ml?

25ml is about 0.845 US fluid ounces, and 50ml is about 1.691 US fluid ounces. In imperial fluid ounces they are about 0.880 and 1.760 respectively.

Can a home jigger be used to sell spirits in a pub?

Do not assume so. UK equipment used for trade is subject to approval and marking requirements. A licensed operator should follow current GOV.UK and local trading-standards guidance.