Biab Water Calculator

BIAB Water Calculator

Calculate the precise water volume needed for your Brew In A Bag (BIAB) brew day.

function calculateBIABWater() { var batchSize = parseFloat(document.getElementById('batchSize').value); var grainWeight = parseFloat(document.getElementById('grainWeight').value); var boilTime = parseFloat(document.getElementById('boilTime').value); var boilOffRate = parseFloat(document.getElementById('boilOffRate').value); var trubLoss = parseFloat(document.getElementById('trubLoss').value); var grainAbsorption = parseFloat(document.getElementById('grainAbsorption').value); if (isNaN(batchSize) || isNaN(grainWeight) || isNaN(boilTime) || isNaN(boilOffRate) || isNaN(trubLoss) || isNaN(grainAbsorption) || batchSize <= 0 || grainWeight <= 0) { document.getElementById('result').innerHTML = 'Please enter valid, positive numbers for all fields.'; return; } var waterAbsorbedByGrain = grainWeight * grainAbsorption; var totalBoilOff = (boilTime / 60) * boilOffRate; var preBoilVolume = batchSize + totalBoilOff + trubLoss; var totalMashWater = preBoilVolume + waterAbsorbedByGrain; var resultHTML = '

Your BIAB Water Requirements

'; resultHTML += 'Total Strike Water Needed: ' + totalMashWater.toFixed(2) + ' Gallons'; resultHTML += '

Volume Breakdown:

'; resultHTML += '

'; resultHTML += '
• Target Batch Volume (in Fermenter): ' + batchSize.toFixed(2) + ' Gallons
'; resultHTML += '
• Water Lost to Grain Absorption: ' + waterAbsorbedByGrain.toFixed(2) + ' Gallons
'; resultHTML += '
• Water Lost to Boil-Off: ' + totalBoilOff.toFixed(2) + ' Gallons
'; resultHTML += '
• Water Lost in Kettle/Trub: ' + trubLoss.toFixed(2) + ' Gallons
'; resultHTML += '

'; resultHTML += '

Key Volume Checkpoints:

'; resultHTML += '

'; resultHTML += '
• Required Pre-Boil Volume: ' + preBoilVolume.toFixed(2) + ' Gallons
'; resultHTML += '

'; document.getElementById('result').innerHTML = resultHTML; }

Master Your Brew Day: The BIAB Water Calculator Explained

Brew In A Bag (BIAB) has revolutionized homebrewing by simplifying the all-grain process. However, one of the most critical steps to ensure a successful brew day is accurately calculating your starting water volume. Hitting your numbers—from mash thickness to pre-boil volume—is key to achieving your target original gravity and final batch size. This calculator is designed to eliminate the guesswork.

Why is Water Calculation So Important for BIAB?

Unlike traditional three-vessel systems that use sparging (rinsing the grains) to collect wort, BIAB is typically a full-volume mash method. This means all the water for the entire process is added at the very beginning. If you miscalculate:

• Too much water: You'll end up with a diluted, low-gravity wort, resulting in a weaker beer than intended.
• Too little water: Your wort will be overly concentrated, and you may not hit your target batch size after accounting for boil-off and other losses.

Understanding the Calculator's Inputs

To get an accurate result, you need to provide a few key details about your recipe and equipment:

• Target Batch Size: This is the final amount of wort you want to transfer into your fermenter. A standard homebrew batch is 5 gallons.
• Total Grain Weight: The combined weight of all the malts and grains in your recipe. More grain will absorb more water.
• Boil Time: The duration of your boil, typically 60 or 90 minutes. Longer boils result in more water evaporation.
• Boil-Off Rate: This is specific to your kettle and heat source. It's the amount of water that evaporates per hour during a rolling boil. To find yours, boil a known volume of water (e.g., 5 gallons) for an hour and measure how much is left.
• Kettle & Trub Loss: The volume of wort left behind in the kettle after you transfer to the fermenter. This "dead space" is filled with hop debris and coagulated proteins (trub). 0.5 gallons is a common estimate.
• Grain Absorption Rate: Grains act like a sponge, soaking up and retaining water. A widely accepted industry standard is approximately 0.125 gallons per pound of grain.

Example Calculation

Let's calculate the water needed for a typical 5-gallon American Pale Ale recipe:

• Target Batch Size: 5.0 Gallons
• Total Grain Weight: 11 lbs
• Boil Time: 60 minutes
• Boil-Off Rate: 1.0 Gallon/Hour
• Kettle & Trub Loss: 0.5 Gallons
• Grain Absorption Rate: 0.125 Gal/lb

The Math:

1. Water Lost to Grain: 11 lbs * 0.125 Gal/lb = 1.375 Gallons
2. Water Lost to Boil: (60 min / 60) * 1.0 Gal/hr = 1.0 Gallon
3. Total Water Needed = (Batch Size) + (Trub Loss) + (Boil-Off) + (Grain Absorption)
4. Total Water Needed = 5.0 + 0.5 + 1.0 + 1.375 = 7.88 Gallons

By using this calculator, you can confidently measure out 7.88 gallons of strike water, knowing you'll hit your volume targets and set your brew day up for success.