The Best Hydrometer for Home Brewing in the UK (2026): Choosing and Using One

A hydrometer is the single most useful measuring tool in home brewing, and one of the cheapest. It tells you how much sugar is in your liquid, and by extension how strong your beer, wine, cider or mead will be and whether fermentation has actually finished. If you brew without one you are guessing; with one you are brewing with data. This guide explains what a hydrometer does, how to read it, and how to choose between the traditional glass type and a digital refractometer.

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What a hydrometer actually measures

A hydrometer measures specific gravity (SG) — the density of your liquid compared with pure water, which sits at 1.000. Sugar makes liquid denser, so unfermented wort or must reads high, typically somewhere around 1.040 to 1.100 depending on the recipe. As yeast converts that sugar into alcohol and carbon dioxide, the density falls. A finished beer often lands somewhere around 1.010, and a dry wine or cider can drop to 1.000 or even below.

You take two key readings:

  • Original Gravity (OG) — measured before you pitch the yeast.
  • Final Gravity (FG) — measured when fermentation appears complete.

The difference between them tells you how much sugar was consumed, which is exactly what determines alcohol content.

Calculating ABV

The standard home-brewing formula is straightforward:

ABV ≈ (OG − FG) × 131.25

So if your beer started at 1.050 and finished at 1.010, that is (1.050 − 1.010) × 131.25, which works out to roughly 5.25% ABV. It is an approximation rather than a laboratory measurement, but it is more than accurate enough for home brewing and lets you build recipes to a target strength.

The FG reading has a second, equally important job: it tells you whether fermentation has stopped. If you take a reading, wait two or three days, and the gravity has not changed, fermentation is done and it is safe to bottle. Bottling too early — while sugar is still fermenting — is the classic cause of over-carbonated or, in the worst case, exploding bottles. Your hydrometer is your safety check against that.

How to take a reading

  • Draw a sample into a trial jar (the tall plastic or glass tube most hydrometers are sold with) rather than dropping the hydrometer into your fermenter, which risks contamination.
  • Give the hydrometer a gentle spin to dislodge any clinging bubbles, which otherwise lift it and skew the reading.
  • Read at eye level, at the point where the liquid surface crosses the scale. The liquid climbs the stem slightly (the meniscus); the usual convention is to read at the main flat level of the liquid.
  • Correct for temperature. Hydrometers are calibrated to a specific temperature, commonly 20°C. A reading taken on a hot sample reads slightly low; most home brewers either cool the sample or apply a simple temperature-correction adjustment.

Triple-scale vs narrow-range hydrometers

Most beginners want a triple-scale hydrometer. These show three scales at once — specific gravity, potential alcohol, and often degrees Brix or a “sugar” scale — which makes them versatile for beer, wine, cider and mead alike. They are inexpensive and widely stocked by UK home-brew suppliers.

Narrow-range hydrometers cover a smaller span of gravities with finer graduations, so they are more precise within their range. Some experienced brewers keep a dedicated finishing hydrometer for accurate low-gravity FG readings. For a first hydrometer, though, a good triple-scale model is the sensible all-rounder.

Because glass hydrometers are fragile, many brewers keep a spare — dropping one on a hard floor mid-brew is a rite of passage, and a cracked or chipped stem can no longer be trusted.

Hydrometer vs refractometer

A refractometer is the digital-age alternative: you place a drop or two of liquid on the prism, hold it to the light, and read the gravity off a scale. Its big advantages are that it needs only a tiny sample and gives an instant reading, which makes it excellent for checking gravity during the brew day and for all-grain brewers monitoring their mash and sparge.

The important caveat is that refractometer readings are thrown off by alcohol. Once fermentation has started, the alcohol present distorts the reading, so you cannot simply read FG off a refractometer without applying a correction calculation (plenty of free online calculators do this). For that reason, many brewers use a refractometer for pre-fermentation and brew-day readings and fall back to a glass hydrometer for the final gravity, where accuracy matters most.

Which should you buy?

For most UK home brewers, an inexpensive triple-scale glass hydrometer with a trial jar is the right first purchase — it is cheap, needs no batteries or calibration, and covers everything from a session bitter to a strong mead. Add a refractometer later if you move into all-grain brewing and want fast brew-day readings, keeping the hydrometer for final gravity.

Specifications, calibration temperatures and prices vary between models, so check the current retailer listing before buying, and consider ordering a spare glass hydrometer at the same time — they are cheap, and the day one breaks is always the day you need it.