\n\nThen the full article.\n\nWrite ONLY the article output, nothing else. No explanations, no commentary.”},”uuid”:”cb4382d7-c51c-48b5-bb40-a3b5c165aa42”,”timestamp”:”2026-03-20T22:28:35.288Z”,”userType”:”external”,”entrypoint”:”cli”,”cwd”:”/Users/valentinseurot/Documents/Jarvis/fermentation-tools-mac”,”sessionId”:”67370e67-91bd-4351-a1d0-c75c9a24494c”,”version”:”2.1.79”,”gitBranch”:”HEAD”,”slug”:”rosy-wandering-knuth”} {“parentUuid”:”cb4382d7-c51c-48b5-bb40-a3b5c165aa42”,”isSidechain”:true,”agentId”:”a89401c93cbd981e1”,”message”:{“model”:”claude-opus-4-6”,”id”:”msg_016UT2mAHHMYjDPvdn8P1v3Y”,”type”:”message”,”role”:”assistant”,”content”:[{“type”:”text”,”text”:”\n\nMETA_TITLE: ABV Calculator: OG and FG Explained\nMETA_DESC: Learn how Original Gravity and Final Gravity work together to calculate your beer’s ABV. Practical guide with formulas, examples, and common pitfalls.\nTITLE: ABV Calculator: OG and FG Explained\n\n## TL;DR\n\nYour beer’s alcohol content comes down to two gravity readings: Original Gravity (OG) before fermentation and Final Gravity (FG) after. The difference between these two numbers tells you exactly how much sugar the yeast converted into alcohol. Understanding OG and FG is the single most practical skill you can develop as a homebrewer.\n\n## Why Gravity Readings Matter More Than You Think\n\nEvery homebrewer remembers their first batch. You followed the recipe, pitched the yeast, waited two weeks, and then wondered: "How strong is this, actually?" The answer lives in two simple measurements that bookend your fermentation — Original Gravity and Final Gravity.\n\nThese readings are not just vanity metrics. They tell you whether fermentation is complete, whether your beer is safe to bottle (no bottle bombs, please), and exactly how much alcohol your yeast produced. Without them, you are brewing blind.\n\nIf you have never taken a gravity reading before, start with our guide on How To Use Hydrometer Measure Abv — it covers the hands-on technique step by step. For now, let us focus on what the numbers actually mean.\n\n## What Is Original Gravity (OG)?\n\nOriginal Gravity measures the density of your wort — the sugary liquid — before yeast goes to work. Pure water has a specific gravity of 1.000. When you dissolve malt sugars into water, the density rises. A typical OG for homebrewed beer falls between 1.030 and 1.120, depending on style.\n\nHere is what those numbers look like in practice:\n\n- Light session beer: OG 1.030–1.040\n- Standard ale or lager: OG 1.045–1.060\n- IPA or strong bitter: OG 1.060–1.075\n- Imperial stout or barleywine: OG 1.080–1.120\n\nThe higher your OG, the more fermentable sugar is available, and the higher your potential alcohol. A wort at 1.050 contains roughly 124 grams of sugar per litre (4.4 oz per US gallon). At 1.080, that jumps to about 207 g/L (7.4 oz/gal).\n\nFor a deeper breakdown of what influences your starting gravity and how to hit your target numbers consistently, check out our Original Gravity Guide Homebrewers.\n\n### How to Measure OG\n\nYou take your OG reading after the boil, once the wort has cooled to around 20°C (68°F). Temperature matters because hydrometers are calibrated to a specific temperature — usually 15.6°C or 20°C (60°F or 68°F). A reading taken at 38°C (100°F) will be artificially low and throw off your final ABV calculation.\n\nFor accurate, repeatable readings, a quality triple-scale hydrometer is essential. The

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reads specific gravity, Brix, and potential alcohol on a single instrument, which saves you from juggling conversion charts mid-brew day.\n\n## What Is Final Gravity (FG)?\n\nFinal Gravity is the density of your beer after fermentation is complete. The yeast has consumed the fermentable sugars and produced alcohol and CO₂. Since alcohol is less dense than water (ethanol has a specific gravity of 0.789), your FG will always be lower than your OG.\n\nTypical FG ranges:\n\n- Dry beer (Belgian tripel, brut IPA): FG 1.002–1.008\n- Medium body (pale ale, amber): FG 1.010–1.016\n- Full body (stout, scotch ale): FG 1.014–1.022\n- Very sweet (milk stout, doppelbock): FG 1.018–1.030\n\nA beer that starts at 1.050 and finishes at 1.010 has undergone healthy, complete fermentation. The same beer finishing at 1.024 suggests a stuck fermentation — the yeast gave up early, leaving residual sweetness and lower alcohol than expected.\n\n### When Is Fermentation Actually Done?\n\nThis is a critical question, especially before bottling. Take FG readings on two consecutive days. If the number is identical both times, fermentation is complete. Do not rely on airlock activity alone — a silent airlock does not always mean the yeast is finished. CO₂ can escape through imperfect seals, giving you a false sense of completion while sugar remains.\n\n## The ABV Formula: Turning Two Numbers Into Alcohol Content\n\nThe standard formula used by homebrewers worldwide is:\n\nABV = (OG − FG) × 131.25\n\nThis is a simplified version derived from the work of brewing scientists, and it is accurate within ±0.1% ABV for beers in the 3–8% range. For stronger beers above 8%, a more precise formula accounts for the non-linear relationship between sugar and alcohol production:\n\nABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794)\n\nLet us run a real example. Say you brewed an American pale ale:\n\n- OG: 1.054\n- FG: 1.012\n- Simple formula: (1.054 − 1.012) × 131.25 = 5.51% ABV\n- Advanced formula: (76.08 × 0.042 / (1.775 − 1.054)) × (1.012 / 0.794) = 5.63% ABV\n\nThe difference is small at this strength. For an imperial stout at OG 1.098 and FG 1.020, the gap widens: the simple formula gives 10.24% while the advanced formula gives 10.72%. Half a percentage point matters when you are pushing into high-gravity territory.\n\n🍺ABV CalculatorCalculate your alcohol by volume from gravity readings\n\n## Apparent Attenuation: The Number Behind the Number\n\nAttenuation tells you what percentage of the available sugar the yeast actually consumed. The formula is:\n\nApparent Attenuation = ((OG − FG) / (OG − 1.000)) × 100\n\nFor our pale ale example: ((1.054 − 1.012) / (1.054 − 1.000)) × 100 = 77.8%\n\nMost ale yeasts attenuate between 72% and 80%. Saison strains can push past 90%. Knowing your yeast’s expected attenuation range helps you predict FG before you even brew. If a recipe calls for OG 1.060 and you are using a yeast with 75% apparent attenuation, you can expect an FG around 1.015.\n\nThis is especially useful when comparing styles. For a full breakdown of typical ABV and gravity ranges across dozens of beer styles, see our Homebrew Abv By Beer Style.\n\n## Common Pitfalls and How to Avoid Them\n\n### Reading at the Wrong Temperature\n\nA hydrometer reading taken at 30°C (86°F) instead of the calibrated 20°C (68°F) will read approximately 0.002 lower than the actual gravity. For a beer with an OG of 1.050, that error translates to roughly 0.26% ABV — enough to matter. Always cool a sample to the correct temperature, or use an online correction calculator.\n\n### Confusing Gravity Points With Specific Gravity\n\nWhen brewers say "fifty gravity points," they mean 1.050, not 50.000. This shorthand is common in recipes and forums. One gravity point equals 0.001 on the specific gravity scale.\n\n### Not Accounting for Non-Fermentable Sugars\n\nLactose, certain crystal malts, and dextrins contribute to OG but yeast cannot ferment them. A milk stout with 0.45 kg (1 lb) of lactose per 19 L (5 gal) batch will have a higher FG — not because fermentation stalled, but because those sugars were never available to the yeast. Your ABV calculation remains valid; the gravity difference still reflects only the sugars that were actually fermented.\n\n### Trub and Sediment Interference\n\nIf your hydrometer sample contains hop debris or yeast sediment, the reading can skew high. Always let the sample settle for a minute, or strain it through a fine mesh before measuring.\n\n## OG and FG Across Brewing Traditions\n\nDifferent brewing cultures approach gravity differently. British brewers historically used the "degrees of gravity" system, where 1.040 is expressed as 40 degrees. Belgian brewers lean on the Plato scale, where 1.048 equals approximately 12°P. German brewers use Plato almost exclusively — the Reinheitsgebot-era tax system was based on it.\n\nThe conversions:\n\n| Specific Gravity | Plato (°P) | Brix (pre-fermentation) |\n|-----------------|-----------|------------------------|\n| 1.040 | 10.0 | 10.0 |\n| 1.050 | 12.4 | 12.4 |\n| 1.060 | 14.7 | 14.7 |\n| 1.080 | 19.3 | 19.3 |\n\nPlato and Brix are nearly identical for unfermented wort. After fermentation, Brix readings from a refractometer require a correction factor because alcohol bends light differently than sugar — a common source of error for brewers who use refractometers for FG.\n\n## Practical Takeaways\n\n1. Always take both readings. OG without FG is half the story.\n2. Record everything. A brewing log with gravity data lets you reproduce your best batches and troubleshoot your worst.\n3. Use the right tool for the job. A hydrometer is more accurate than a refractometer for FG readings unless you apply a correction formula.\n4. Confirm fermentation is done with consecutive-day FG readings before bottling.\n5. Match your expectations to your yeast. Attenuation ranges vary by strain — check the manufacturer’s specs.\n\nThis article contains affiliate links. If you purchase through these links, we may earn a small commission at no extra cost to you. This helps support abv-calculator.com and keeps our tools free.\n\n## Methodology\n\nABV formulas referenced in this article follow the standard simplified equation (OG − FG) × 131.25, originally derived from the stoichiometry of ethanol fermentation (Gay-Lussac, 1810), and the alternate formula published by Balling and later refined by Hall (Zymurgy, 1995). Attenuation calculations use the apparent attenuation method as defined by the American Society of Brewing Chemists (ASBC Methods of Analysis, Beer-6). Gravity-to-Plato conversions follow the ASBC polynomial approximation. Typical gravity and attenuation ranges for yeast strains and beer styles are sourced from the 2021 BJCP Style Guidelines and manufacturer datasheets from Fermentis, Lallemand, and White Labs. Sugar density values are based on the ICUMSA sucrose density tables adapted for brewing wort composition.”}],”stop_reason”:”end_turn”,”stop_sequence”:null,”usage”:{“input_tokens”:3,”cache_creation_input_tokens”:1671,”cache_read_input_tokens”:7439,”output_tokens”:2748,”server_tool_use”:{“web_search_requests”:0,”web_fetch_requests”:0},”service_tier”:”standard”,”cache_creation”:{“ephemeral_1h_input_tokens”:0,”ephemeral_5m_input_tokens”:1671},”inference_geo”:”“,”iterations”:[],”speed”:”standard”}},”requestId”:”req_011CZF7zCPzZY53LvtRYrSEo”,”type”:”assistant”,”uuid”:”0ef25e61-f1dd-4fcd-8c9b-6f669213a8c6”,”timestamp”:”2026-03-20T22:29:36.448Z”,”userType”:”external”,”entrypoint”:”cli”,”cwd”:”/Users/valentinseurot/Documents/Jarvis/fermentation-tools-mac”,”sessionId”:”67370e67-91bd-4351-a1d0-c75c9a24494c”,”version”:”2.1.79”,”gitBranch”:”HEAD”,”slug”:”rosy-wandering-knuth”}