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The reference changes the target box and dial-in aim, not the measured brew.
Enter the dose weighed into the brewer or portafilter.
g
Use cup liquid mass, not the water poured into the brewer.
g
Choose the scale shown by the refractometer.
The default 0.85 is an editable planning assumption.
×
Center is the neutral reference; lower and upper stay inside the same box.
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%
g/mL
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Coffee strength describes how much dissolved coffee material is present in the finished drink. A refractometer reports that concentration as total dissolved solids (TDS), usually as a percentage. Extraction yield answers a different question: what percentage of the dry coffee dose moved into the beverage.

Two brews can have the same strength and different extraction yields because strength depends on the concentration in the cup, while extraction also depends on the beverage mass and dry dose. A short espresso can be far more concentrated than filter coffee without extracting a larger share of the grounds.

MeasureWhat it describesMain influences
TDSConcentration of dissolved coffee solids in the drinkExtracted solids and finished beverage mass
Extraction yieldShare of the dry dose dissolved into the beverageDissolved solids and dry coffee dose
In-cup mass ratioFinished beverage mass per unit of dry coffeeCup liquid mass and dose

Reference boxes help describe a brew, but they do not guarantee flavor quality or personal preference. Roast level, grind distribution, water chemistry, temperature, contact time, agitation, filtration, and measurement technique can all change taste or the reliability of a reading. Treat a reference position as evidence for dialing in, then confirm the next change by tasting and measuring again.

How to Use This Tool:

Start with a temperature-stable, well-mixed sample and select the comparison reference that matches the brewing method.

  1. Choose Filter, Espresso, or Immersion. This changes the reference box and dial-in aim, not the measured brew.
  2. Enter the Dry coffee dose and the Finished beverage mass. Use liquid in the cup, including any bypass water already mixed in, rather than the water originally poured.
  3. Enter the Meter reading and choose % TDS or °Bx. For Brix, replace the default conversion factor if the meter or measurement method documents a different value.
  4. Select a Dial-in aim inside the reference box. Use Reading correction only for a documented calibration adjustment; beverage density changes only the approximate milliliter display.
  5. Read the strength and extraction position together. If the inputs imply more than 100% extraction or corrected TDS outside 0% to 30%, recheck the scale, dose, and beverage mass before using the result.

Interpreting Results:

Read Effective strength and Extraction yield as two coordinates. A brew may be within the selected strength range but below or above the extraction range, or the reverse. The Brew map makes that distinction visible.

  • Within both ranges means the measurement lies inside the selected reference box, including its boundary values. It is not a taste verdict.
  • Below or above strength describes concentration. Dilution or a change in beverage mass can move strength without preserving extraction.
  • Below or above extraction describes dissolved solids relative to dose. Grind, contact time, wetting, and agitation may change it, but the direction and size of a useful adjustment depend on the brew.
  • Dial in plan gives mass-balance targets. Measure the next brew rather than assuming the suggested mass alone will reproduce the target or improve flavor.

Technical Details:

TDS is a mass fraction expressed as a percentage. The calculation first converts a Brix reading when necessary, applies an optional percentage correction, and then uses mass conservation to estimate dissolved solids and extraction yield. Full precision is retained through the calculations; the main strength and extraction displays are rounded to two decimal places.

Formula Core

For a direct TDS reading, the scale factor is 1. For Brix, it is the selected Brix-to-TDS factor.

Teff=Rf(1+c100)

The effective TDS fraction determines the mass of dissolved coffee solids. Extraction yield then compares that solids mass with the dry dose.

ms=mbTeff100 E=msmd×100
  • R is the meter reading, f is 1 or the Brix conversion factor, and c is the reading correction in percent.
  • Teff is effective TDS in percent; mb, ms, and md are beverage, dissolved-solids, and dry-dose masses in grams.
  • E is extraction yield in percent. The in-cup mass ratio is mb ÷ md.

With a 20 g dose, a 320 g beverage, and 1.35% effective TDS, dissolved solids are 4.32 g and extraction yield is 21.60%. The in-cup mass ratio is 1:16.

Reference and Rule Core

ReferenceTDSExtractionBasis
Filter1.15% to 1.45%18% to 22%SCA reference
Espresso9% to 15%18% to 22%SCA equipment reference
Immersion1.20% to 1.55%18% to 22%Planning range, not an SCA standard

Values equal to a lower or upper edge count as within the range. The lower-quarter, center, and upper-quarter aims sit 25%, 50%, and 75% of the way from each lower edge to its upper edge.

A strength-only beverage target holds current dissolved-solids mass constant and divides it by the target TDS fraction. The combined target instead uses the target extraction to obtain target solids mass, then divides by target TDS. These are planning identities, not predictions of how a grind or technique change will affect the next brew.

Accuracy Notes:

The arithmetic can be precise while the measurement is not. Cool and mix the sample as required by the refractometer, remove suspended particles when the measurement method calls for it, keep the prism clean, and use the conversion factor documented for the meter and coffee workflow.

  • The default Brix-to-TDS factor of 0.85 is an editable planning assumption, not a universal conversion.
  • Finished beverage mass excludes water retained by the grounds; replacing it with poured-water mass changes extraction yield.
  • Beverage density affects only the approximate volume in milliliters. It does not change the mass-based strength or extraction calculation.
  • Reference boxes describe measurements and cannot account for roast, water, sensory preference, or defects in sampling and calibration.

References: