TDS Strength Calculator
Refractometer reading → strength in mg/mL + SCA Golden Cup band. Add extraction yield to plot both SCA chart axes.
Refractometer reading of your brewed coffee (coffee-calibrated; not raw Brix)
Grams of water per gram of coffee (e.g., 16 = 16 g water : 1 g coffee)
Enter if known: plots both SCA axes for a full chart position
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How to Use This Calculator
Take a Refractometer Reading
Brew your coffee and let a small sample cool. Take a TDS reading with a coffee-calibrated refractometer: VST, DiFluid R2, or Atago PAL-COFFEE. Enter the % value. Default is 1.25%, the SCA midpoint for filter coffee.
Enter Your Brew Ratio
Enter grams of water per gram of coffee. 16 is the SCA reference ratio for filter (1:16 water:coffee). This is context, not a formula input: the calculator uses it to frame your setup.
Add Extraction Yield (Optional)
If you have an extraction yield reading from the same brew, enter it here. The calculator will plot both axes of the SCA Brewing Control Chart and tell you where you land relative to the Golden Cup target.
What TDS Tells You
TDS answers “how strong is this?” The SCA Golden Cup target is 1.15–1.35% for filter coffee, a reference anchor, not a verdict. It was set for North American taste preferences in the 1990s. Nordic specialty commonly targets 1.20–1.50% and considers it dialled in.
TDS separates strength from extraction. A 1.30% TDS cup can be under-extracted (bright and acidic) or over-extracted (bitter). TDS tells you how much dissolved; extraction yield tells you whichcompounds dissolved. That’s why the SCA Brewing Control Chart uses both axes: TDS alone only gives you half the picture.
The mg/mL conversion is useful if you think in concentration units: 1.25% TDS = 12.5 mg of dissolved coffee solids per mL. A standard 240 mL cup at 1.25% contains about 3 g of dissolved coffee, out of the 15 g dose at 20% extraction yield. To work backwards from a target TDS to a dose, use the Coffee to Water Ratio Calculator.
Glossary
- TDS (Total Dissolved Solids):
- Concentration of dissolved coffee solids in the brewed liquid, measured as a percentage by refractometer.
- Strength (mg/mL):
- TDS expressed as milligrams of dissolved solids per millilitre of liquid. 1% TDS = 10 mg/mL.
- SCA Golden Cup Standard:
- SCA's recommended brewing targets: 1.15–1.35% TDS, 18–22% extraction yield for filter coffee.
- Brew Ratio:
- Ratio of brew water to coffee by mass; expressed W:C for filter coffee (e.g., 16:1 = 16 g water per 1 g coffee).
- SCA Brewing Control Chart:
- Diagram mapping TDS% (strength) and extraction yield% to quality zones: ideal, under/over-extracted, weak/strong.
- Extraction Yield:
- Percentage of the dry coffee dose that dissolved into the brewed liquid. Calculated from dose, beverage mass, and TDS.
Frequently Asked Questions
What is TDS in coffee?
TDS stands for Total Dissolved Solids: the concentration of coffee compounds dissolved in your brewed liquid, measured as a percentage by refractometer. A reading of 1.25% means 1.25 g of dissolved coffee solids per 100 mL of liquid, or 12.5 mg/mL.
What is the SCA Golden Cup target for TDS?
The Specialty Coffee Association's recommended TDS range for filter coffee is 1.15–1.35%. This was established from sensory research on North American preferences and is used as a reference point across the industry: not a universal guarantee of quality.
Why does this calculator convert TDS% to mg/mL?
mg/mL (milligrams per millilitre) is a direct concentration unit. 1% TDS = 10 mg/mL, because water is approximately 1 g/mL. Some brewers and researchers prefer mg/mL because it doesn't require translating percentages: a 240 mL cup at 1.25% TDS contains exactly 3 g of dissolved coffee.
What's the difference between TDS (strength) and extraction yield?
TDS tells you how much dissolved. Extraction yield tells you what fraction of your coffee dose dissolved. You can hit the same TDS at different extraction yields by changing your dose, ratio, or brew time. The SCA Brewing Control Chart uses both axes because a cup can be the right strength but under- or over-extracted.
My TDS reads 1.50%: is that too strong?
By SCA filter standards, yes: 1.50% is above the 1.15–1.35% ideal window. But the SCA target was set for North American taste preferences. Nordic specialty roasters often target 1.20–1.50% and consider it dialled in. Whether it's too strong depends on the coffee, the roast, and the palate.
Does this calculator work for espresso?
No. Espresso TDS runs 6–12%. This calculator is calibrated for filter coffee (1–2% TDS). Espresso readings will trigger an out-of-range warning: intentionally.
What refractometer should I use?
Coffee-calibrated refractometers apply a correction factor for coffee solubles (as opposed to sucrose). The main options: VST Coffee Refractometer (~$400), DiFluid R2 Extract (~$100), Atago PAL-COFFEE (~$200).
A raw Brix refractometer will give a different reading for the same sample. If you're using Brix, look up the conversion factor for your specific model.
What does the SCA Brewing Control Chart show?
The SCA Brewing Control Chart plots TDS% (strength) on the Y-axis and extraction yield% on the X-axis, with the Golden Cup zone at the intersection of 1.15–1.35% TDS and 18–22% extraction. It helps diagnose whether a problem cup is a strength issue, an extraction issue, or both.