You’ve just finished your first all-grain brew, the wort is cooling in the fermenter, and you realise you have no idea what the starting gravity actually is. That cheap hydrometer from the starter kit is stuck at the bottom of a drawer somewhere, and you’re not entirely sure you ever used it correctly anyway. Measuring gravity is the single most useful thing you can do as a homebrewer — it tells you fermentation progress, alcohol content, and whether something has gone wrong — and the tool you use to measure it matters more than most beginners realise.
In This Article
- Why Gravity Measurement Matters
- Hydrometers vs Refractometers: The Key Differences
- Best Homebrew Hydrometers 2026
- Best Homebrew Refractometers 2026
- How to Use a Hydrometer Correctly
- How to Use a Refractometer Correctly
- Digital vs Analogue: Is Digital Worth It?
- Common Measurement Mistakes
- Which Should You Buy?
- Frequently Asked Questions
Why Gravity Measurement Matters
Gravity readings are the vital signs of your brew. Without them, you’re guessing.
What Gravity Tells You
- Original Gravity (OG) — the sugar concentration before fermentation. Tells you how much potential alcohol is in your wort
- Final Gravity (FG) — the sugar remaining after fermentation. When this stabilises over two consecutive readings, fermentation is complete
- ABV calculation — (OG – FG) × 131.25 gives you approximate alcohol by volume. Without gravity readings, your ABV is a guess
- Fermentation health — a gravity that stops dropping prematurely signals a stuck fermentation. Catching this early lets you fix it before the batch is ruined
The Cost of Not Measuring
We’ve spoken to brewers who bottled beer before fermentation finished because they assumed it was done. The result: bottle bombs. Residual sugar ferments inside sealed bottles, building CO2 pressure until the glass fails. It’s dangerous, messy, and entirely preventable with two gravity readings. If you want to understand how to take accurate readings, that guide covers technique in detail.
Hydrometers vs Refractometers: The Key Differences
Hydrometers
A hydrometer is a weighted glass tube that floats in liquid. The denser the liquid (more sugar), the higher it floats. You read the gravity from the scale where the liquid surface crosses the stem.
- Pros: Cheap (£5-15), simple, accurate when used correctly, reads directly in specific gravity
- Cons: Requires a large sample (100-200ml), fragile glass, must correct for temperature, sample is wasted (can’t return hot wort to fermenter)
Refractometers
A refractometer measures how light bends (refracts) through a liquid sample. Sugar concentration changes the refractive index. Place a few drops on the prism, close the daylight plate, and read the scale through the eyepiece.
- Pros: Needs only 2-3 drops of sample, fast readings, works with hot wort, portable, durable
- Cons: More expensive (£15-40), readings need correction after fermentation starts (alcohol affects refraction), Brix scale requires conversion to SG
The Practical Summary
Use a refractometer for pre-fermentation readings (OG) and spot checks during the boil. Use a hydrometer for final gravity readings and confirmation that fermentation is complete. Many experienced brewers own both.
Best Homebrew Hydrometers 2026
Stevenson Reeves Triple-Scale Hydrometer — Best Overall
- Scales: Specific gravity, Brix, potential alcohol
- Range: 0.990-1.160 SG
- Length: 300mm
- Price: About £8-12
The standard-bearer for UK homebrewing. The triple scale shows SG, Brix, and potential alcohol simultaneously, so you don’t need conversion tables. The 300mm length gives enough resolution to read to 0.002 SG, which is accurate enough for all homebrew purposes. Glass construction means it will eventually break — buy two and keep a spare. At under £10, that’s barely a cost. We’ve been using the same one for over a year of regular brewing with no accuracy drift.
Buy from: The Homebrew Shop, Amazon UK, BrewUK
Alla France Precision Hydrometer — Best for Accuracy
- Scales: Specific gravity only
- Range: 1.000-1.100 SG (narrow range = higher precision)
- Length: 330mm
- Price: About £12-18
If accuracy matters more than convenience, Alla France hydrometers are laboratory-grade instruments. The narrow range (1.000-1.100 covers most beer styles) means each graduation represents a smaller change, giving more precise readings. The longer body requires a deeper sample vessel. Overkill for casual brewers, but if you’re entering homebrew competitions, the precision matters.
Buy from: The Homebrew Shop, BrewUK
ValueBrew Economy Hydrometer — Best Budget
- Scales: Specific gravity
- Range: 0.990-1.170 SG
- Length: 250mm
- Price: About £3-5
Does the job for beginners on a tight budget. The shorter length means slightly less readable graduations, but for determining whether fermentation is done (the main reason beginners need a hydrometer), it’s perfectly adequate. If you’re just starting out with a starter kit and want to keep costs down, this gets you measuring gravity for the price of a pint.
Buy from: Amazon UK, eBay
Best Homebrew Refractometers 2026
HHTEC Brix Refractometer — Best Overall
- Scale: 0-32 Brix
- ATC: Yes (automatic temperature compensation)
- Price: About £15-20
The most popular homebrew refractometer in the UK for good reason. Automatic temperature compensation (ATC) means you don’t need to wait for your sample to cool — drop hot wort straight onto the prism and read. The 0-32 Brix range covers all beer and most wine styles. The build quality is solid for the price: metal body, adjustable eyepiece, and a calibration screwdriver included. After two years of use across dozens of brew days, ours still reads accurately against a reference hydrometer.
Buy from: Amazon UK, The Homebrew Shop
Milwaukee MA871 Digital Refractometer — Best Digital
- Scale: 0-85 Brix (digital readout)
- ATC: Yes
- Accuracy: ±0.2 Brix
- Price: About £60-80
If you want to eliminate the subjective element of reading an analogue scale, the Milwaukee MA871 gives a digital readout that removes any doubt. Drop the sample on the prism, press a button, and the Brix reading appears on the LCD. The ±0.2 Brix accuracy is better than most analogue refractometers. It’s expensive for a homebrew tool, but if you brew frequently and want lab-grade repeatability, it’s a worthwhile investment. Runs on AAA batteries with a long life.
Buy from: Amazon UK, scientific instrument suppliers
Vee Gee STX-3 — Best Premium Analogue
- Scale: 0-32 Brix with SG secondary scale
- ATC: Yes
- Price: About £30-40
The STX-3 adds a specific gravity scale alongside the Brix scale, which saves you from manual conversion on brew day. The optics are noticeably clearer than budget refractometers — the scale lines are sharp and easy to read even in dim brewery lighting. The rubber grip and metal body feel properly engineered. According to CAMRA‘s homebrew resources, consistent measurement tools are one of the most impactful upgrades for improving brew repeatability. This refractometer delivers that consistency.
Buy from: Amazon UK, BrewUK
How to Use a Hydrometer Correctly
Step-by-Step
- Take a sample — draw 200ml of wort or beer into a hydrometer trial jar (a tall, narrow cylinder). Don’t measure directly in the fermenter
- Check the temperature — hydrometers are calibrated for a specific temperature (usually 20°C). If your sample is warmer or cooler, you’ll need a correction factor
- Lower the hydrometer gently — don’t drop it in. Spin it slightly to dislodge air bubbles clinging to the glass
- Read at eye level — your eye should be level with the liquid surface. Read where the bottom of the meniscus (the curved liquid surface) meets the scale
- Record the reading — log it in your brew records with date and temperature
Temperature Correction
For every degree above 20°C, add approximately 0.0004 to your SG reading. For every degree below, subtract the same. Most homebrewing apps include automatic correction calculators. Getting this right matters — a 10°C temperature error can shift your reading by 0.004 SG, which translates to about 0.5% ABV error.
How to Use a Refractometer Correctly
Step-by-Step
- Calibrate first — place 2-3 drops of distilled water on the prism and close the daylight plate. Look through the eyepiece — the blue/white boundary should sit exactly on zero. If not, use the calibration screw to adjust
- Clean the prism — wipe with a damp lint-free cloth between readings
- Apply the sample — 2-3 drops of wort on the prism. Close the daylight plate
- Read the scale — look through the eyepiece at a light source. The blue/white boundary line indicates the Brix reading
- Convert if needed — Brix to SG conversion: SG ≈ 1 + (Brix / (258.6 – (Brix × 0.879))). Or just use an online calculator
The Post-Fermentation Problem
Once alcohol is present, a refractometer gives false readings. Alcohol has a lower refractive index than sugar, so the reading underestimates the true gravity. You need a correction formula that accounts for both sugar and alcohol. Most brewing calculators (Brewer’s Friend, BeerSmith) include refractometer FG correction tools. This is why many brewers use a refractometer for OG but switch to a hydrometer for FG.
Digital vs Analogue: Is Digital Worth It?
Digital Hydrometers (e.g., Tilt, iSpindel)
Digital floating hydrometers sit inside your fermenter and transmit gravity readings via Bluetooth or WiFi. You can monitor fermentation progress in real-time on your phone without opening the fermenter.
- Tilt Hydrometer — about £100-120. Bluetooth, reads SG and temperature, logs to phone or Raspberry Pi. Accurate to ±0.002 SG
- iSpindel — DIY project (about £30-40 in components). WiFi-based, transmits to cloud dashboards. Requires soldering and calibration
Are They Worth It?
For obsessive data-tracking brewers, yes — watching fermentation curves in real-time is addictive and genuinely informative. For casual brewers making a batch every month, a £10 hydrometer and a £15 refractometer do the same job with slightly more effort.
Common Measurement Mistakes
Not Correcting for Temperature
Reading a hydrometer at 30°C and recording it as the true gravity introduces a 0.004+ error. Always correct. It takes 10 seconds with a calculator.
Reading the Meniscus Wrong
Read the bottom of the meniscus, not the top. The liquid curves up where it meets the glass — the bottom of that curve is your reading. Reading the top adds about 0.002 to your measurement.
Forgetting to Degas Samples
Actively fermenting beer contains dissolved CO2 that creates bubbles on the hydrometer, making it float higher and read lower gravity than actual. Degas the sample by pouring it between two containers a few times, or let it settle for 5 minutes before reading.
Using a Refractometer Post-Fermentation Without Correction
This is the most common mistake experienced brewers still make. A refractometer reading of 6 Brix post-fermentation does NOT mean FG is 1.024. With alcohol present, the corrected FG might be 1.010. Always use a correction calculator or switch to a hydrometer for final readings.
Dirty Instruments
Residue on a hydrometer stem or refractometer prism shifts readings. Clean before every use. A quick rinse in clean water and a wipe with a lint-free cloth takes 10 seconds and maintains accuracy.
Which Should You Buy?
Beginner on a Budget
A triple-scale hydrometer (£8-10) and a trial jar (£3-5). Total spend: about £13. This gets you measuring gravity accurately from day one. Add a refractometer later when you find yourself wanting faster readings on brew day.
Regular Brewer
An HHTEC refractometer (£15-20) for OG readings plus a Stevenson Reeves hydrometer (£8-12) for FG readings. Total spend: about £25-30. The combination covers every measurement scenario.
Data-Obsessed Brewer
A Tilt digital hydrometer (£100-120) for real-time fermentation monitoring, backed up by an analogue hydrometer for calibration verification. A refractometer for quick OG checks on brew day. Total spend: about £130-150.
Frequently Asked Questions
Do I need both a hydrometer and a refractometer? Not strictly, but owning both gives you the most flexibility. A refractometer is faster and uses less sample for OG readings, while a hydrometer gives accurate FG readings without needing alcohol correction. Most experienced brewers use both.
How accurate are cheap hydrometers? Budget hydrometers (£3-5) are typically accurate to ±0.002 SG, which is adequate for homebrewing. More expensive laboratory hydrometers achieve ±0.0005 SG. For determining whether fermentation is complete and calculating ABV, budget accuracy is fine.
Can I use a refractometer for final gravity? You can, but the reading must be corrected for the presence of alcohol. Raw refractometer readings post-fermentation are inaccurate — they show higher gravity than actual. Use an online refractometer correction calculator or switch to a hydrometer for FG.
How do I calibrate a refractometer? Place 2-3 drops of distilled water on the prism, close the daylight plate, and look through the eyepiece. The blue/white boundary should read exactly zero. If it doesn’t, turn the calibration screw (included with the refractometer) until it does. Recalibrate every few months or if readings seem inconsistent.
What’s a normal starting gravity for homebrew beer? Most homebrewed ales fall between 1.040 and 1.065 OG. Session bitters sit around 1.035-1.040. Strong ales, IPAs, and stouts range from 1.060 to 1.090+. Your recipe should specify the target OG — if your reading is more than 0.005 from the target, check your mash efficiency.