Coffee Strength Calculator

Metric	Value	Copy
{{ row.label }}	{{ row.value }}

Coffee strength is the concentration of dissolved coffee material in the cup, and extraction is the share of the dry grounds that ended up in the drink. A coffee extraction yield calculator turns those measurements into numbers you can compare from brew to brew, even when the recipe changes.

By combining the dry coffee dose, the beverage mass you actually brewed, and a refractometer reading of dissolved solids, the calculator estimates strength and extraction together. It then places the result against a target zone so you can see whether you are trending light, heavy, or balanced.

For example, a pour over that tastes thin can show up as low strength even when extraction looks acceptable, which usually points to a larger beverage yield than intended. A harsh finish can show up as extraction above the target zone, which is a cue to adjust grind, contact time, or brew water.

Because the math is a simple mass balance, accuracy depends on careful weighing and a stable sampling routine. Treat target zones as helpful guides rather than proof that a brew will taste good, and recheck your refractometer scale when results look implausible.

If you keep notes for training or quality work, repeat the same base recipe with small changes so the differences in results stay meaningful.

Technical Details:

Total Dissolved Solids (TDS) is the mass fraction of dissolved material in the brewed beverage, commonly reported as a percentage by coffee refractometers. Extraction yield is a mass balance estimate of how much of the dry coffee dose became dissolved solids in the final beverage.

This calculator takes three primary measurements in grams and percent, then derives dissolved solids and extraction yield by multiplication and division. When your refractometer reports degrees Brix (°Bx), it applies a configurable Brix to TDS factor before doing the same mass balance.

Results are interpreted using a brewing control chart that plots extraction yield on the horizontal axis and strength on the vertical axis. Each brew style includes a target box, and the status label is based on whether your point falls inside or outside that box.

Comparisons are most meaningful when you weigh everything, use the same refractometer workflow, and keep the brew style target consistent. The numbers describe concentration and mass transfer, but they do not guarantee a specific taste outcome.

Core equations

The calculator converts a refractometer reading into %TDS, then turns that concentration into dissolved solids and extraction yield.

T = R \times F \times (1 + \frac{c}{100})

\begin{array}{lcl} F & = & 1 for %TDS readings \\ k_{Bx} for °Bx readings \end{array}

\begin{array}{lcl} f & = & \frac{T}{100} \\ m_{s} & = & m_{b} \times f \\ E & = & \frac{m_{s}}{m_{c}} \times 100 \end{array}

\begin{array}{lcl} m_{ret} & = & a \times m_{c} \\ m_{brew} & = & \max (0, m_{b} - m_{by}) + m_{ret} \\ m_{tot} & = & m_{brew} + m_{by} \\ W & = & \frac{m_{tot}}{m_{c}} \\ B & = & \frac{m_{b}}{m_{c}} \end{array}

Symbols and units

Symbols used in the coffee strength and extraction equations
Symbol	Meaning	Unit or datatype	Source
`R`	Refractometer reading value	number	Input
`F`	Scale factor, 1 for %TDS or `k_Bx` for °Bx	number	Input or constant
`c`	Reading correction percent	percent	Input
`T`	Strength as %TDS after conversion and correction	percent	Derived
`m_c`	Dry coffee dose	g	Input
`m_b`	Beverage mass in cup	g	Input
`f`	TDS fraction, `T / 100`	unitless	Derived
`m_s`	Dissolved solids extracted	g	Derived
`E`	Extraction yield	percent	Derived
`a`	Absorption ratio, water retained per gram coffee	g/g	Input
`m_by`	Bypass water added after brewing	g	Input
`W`	Water to coffee ratio	unitless	Derived
`B`	Beverage ratio in cup	unitless	Derived

Worked example

Example input: Filter style, coffee dose 20 g, beverage mass 320 g, refractometer reading 1.35 %TDS, absorption ratio 2.00 g/g, bypass water 0 g.

T = 1.35 \times 1 \times (1 + \frac{0}{100}) = 1.35

f = \frac{1.35}{100} = 0.0135

m_{s} = 320 \times 0.0135 = 4.32 g

E = \frac{4.32}{20} \times 100 = 21.6 %

m_{ret} = 2.00 \times 20 = 40 g

m_{brew} = \max (0, 320 - 0) + 40 = 360 g

W = \frac{360}{20} = 18.00 : 1

With strength 1.35 %TDS and extraction 21.6 %, this point sits inside the filter target box, so the status reads Inside ideal box.

Interpretation and target ranges

Target ranges used to label coffee strength and extraction results
Brew style	TDS lower	TDS upper	Extraction lower	Extraction upper	Label
Filter	1.15	1.45	18	22	SCA filter box
Immersion	1.25	1.55	18	22	Immersion sweet spot
Espresso	8	12	19	23	Modern espresso zone

Values on or within the box edges are treated as inside the ideal box. Values below either lower bound are labeled Under target, and values above either upper bound are labeled Over extracted.

Parameters that shape the estimate

Advanced parameters that affect derived brewing metrics
Parameter	Meaning	Unit or datatype	Typical range	Sensitivity	Notes
Absorption ratio	Brew water retained by the grounds	g/g	Filter beds 1.8–2.3, espresso pucks 1.0–1.3	Medium	Used to estimate brew water from in-cup mass
Bypass water	Water added after brewing for dilution	g	0 and up	High	Removed from the brewed portion before estimating brew water
Brix to TDS factor	Multiplier applied when the device reports °Bx	number	Coffee often 0.85–0.86	High	A warning appears outside 0.75–0.95
Reading correction	Percentage offset for small instrument bias	percent	-5 to 5	Medium	Applied as a multiplier, neutral is 0
Beverage density	Mass to volume conversion for mL display	g/mL	Near 1.0, espresso up to about 1.05	Low	Does not affect extraction, only the volume estimate

Validation and bounds

Input validation and control limits
Field	Type	Min	Max	Step or pattern	Message
Coffee dose	number	0	—	step 0.1	Enter a coffee dose above 0 g.
Beverage mass	number	0	—	step 1	Enter a beverage mass above 0 g.
Refractometer reading	number	0	—	step 0.01	Strength is zero; add a refractometer reading.
Absorption ratio	range	0.5	3	step 0.05	Higher values increase estimated brew water and water ratio.
Bypass water	number	0	—	step 1	Set to 0 for no bypass.
Brix to TDS factor	number	0.6	1.2	step 0.01	Brix conversion looks atypical; common coffee factors are 0.85–0.86.
Reading correction	range	-5	5	step 0.1	Applied as a multiplier, 1 plus correction percent divided by 100.
Beverage density	number	0.9	1.1	step 0.005	Used only for the mL estimate; the calculator clamps density to at least 0.5.
Strength plausibility	derived check	0	15	warning if above 15	TDS is unusually high; recheck the reading scale.

Outputs and formats

Supported export formats and file naming
Output	Accepted families	What you get	Encoding and precision	Rounding
Metrics table	copy or download	CSV with headers `Metric`, `Value`	text, values formatted for display	varies by metric
Report	download	DOCX report titled Coffee Strength Report	text and table rows from the metrics list	formatted strings
Structured payload	copy or download	JSON with `inputs`, `results`, and `status`	UTF-8 JSON, numeric values are unquoted numbers	no display rounding applied
Control chart	download	PNG, WebP, or JPEG image, plus a small CSV summary	image background set to white; JPEG quality 0.92	chart CSV uses 4 decimals

Default filenames include coffee_strength_metrics.csv, coffee_strength_report.docx, coffee_strength.json, and coffee_strength_control_chart with the chosen extension.

Precision, determinism, and performance

Strength and extraction are computed with standard floating point arithmetic and are deterministic for identical inputs. Display formatting typically uses 2 decimals for strength and extraction, 2 decimals for ratios, and metric-specific rounding for supporting values.

Chart rendering is debounced and updates after short input pauses, and the chart is drawn as scalable vector graphics for sharp zooming. The computation itself is constant time and does not grow with input size.

Security, privacy, and compliance

The calculator logic runs browser-based and does not send your numeric inputs to an application server. Copy actions write to the system clipboard, and downloads save files to your device using standard browser mechanisms.

Because inputs are numeric and outputs are derived from those numbers, the risk of script injection through user input is low. Treat copied exports as potentially sensitive in a workplace setting, since any clipboard contents may be visible to other applications.

Assumptions and limitations

All mass inputs are treated as grams, and concentration inputs are treated as percent.
Extraction yield assumes dissolved solids are evenly represented by the refractometer sample.
The Brix to TDS factor is an empirical multiplier, not a physics-based conversion.
Reading correction is a simple percentage multiplier and does not model temperature compensation curves.
Absorption is modeled as a fixed ratio per gram of coffee, not a time-dependent process.
Bypass water is assumed to be added after brewing and does not affect extraction in the model.
Target boxes are reference ranges for each brew style and are not personalized to your coffee.
Heads-up A very tight ratio can be labeled Over extracted even when extraction yield is moderate.
The volume in mL is an estimate based on density and does not affect any other metric.

Edge cases and common error sources

Zero or negative inputs are clamped to 0, so results do not appear until key values are above 0.
NaN or Infinity from invalid arithmetic is treated as 0 for strength before reporting.
Strength above 15 %TDS triggers a warning, since it often indicates the wrong reading scale.
Using °Bx mode with an extreme factor can inflate or deflate strength and extraction dramatically.
Bypass water greater than beverage mass makes brewed mass clamp to 0 in the brew water estimate.
Very small doses magnify rounding effects and can make extraction yield unstable.
Signed zero and tiny floating point values near zero can flip the resultsReady gate in edge situations.
Rounding ties and display precision can hide small changes when you are tuning in small steps.
Chart axis limits adapt to your point and the target box, so comparisons should use exported numbers.
Clipboard writes can fail if the browser blocks permissions, leaving copy buttons seemingly unresponsive.
Stale cached assets can affect chart rendering if the charting layer script fails to load.
Rapid input changes can briefly show outdated chart state until the debounce interval completes.

Background references

For context, compare results to the Specialty Coffee Association brewing control chart concept, refractometer guidance for coffee measurement, and basic mass balance models used in brewing education.

Step-by-Step Guide:

Strength and extraction become actionable when you measure dose, beverage yield, and dissolved solids in a consistent way.

Choose a brew style preset that matches your recipe.
Enter Coffee dose as the dry grounds mass.
Enter Beverage mass as the in-cup yield after brewing.
Enter Refractometer reading and select the correct scale.
If you diluted after brewing, set Bypass water to that added amount.
Review strength, extraction, and the status label, then adjust your recipe and repeat.

Quick example: Dose 20 g, beverage 320 g, reading 1.35 %TDS returns strength 1.35 %TDS and extraction 21.6 %.

If your device reports °Bx, keep the Brix to TDS factor near 0.85 to 0.86 unless you have a better calibration.
Weigh the beverage after brewing, not before, and avoid estimating volume from cup markings.
Mix the sample well before measuring, since crema and fines can skew refractometer readings.

Pro tip: log both strength and extraction together, because either number alone can be misleading.

Once your point sits inside the target box, use small changes to keep flavor consistent across batches.

FAQ:

Is my data stored?

Calculations run on the client and the included logic does not send your inputs to an application server. Copies and downloads only exist where you paste or save them. A charting script may be loaded as a static page asset, but your brew numbers are not uploaded.

How accurate are results?

The math is a direct mass balance, so the main error sources are weighing, refractometer calibration, sample temperature, and choosing the wrong scale. Treat extraction yield as an estimate for comparison, not a lab-grade truth. Repeat the same recipe and change one variable at a time for the clearest signal.

What units should I use?

Enter coffee dose, beverage mass, and bypass water in grams. Enter refractometer strength as %TDS or °Bx, and enter density in g/mL if you want a volume estimate. Outputs report percent for strength and extraction, and ratios as X : 1.

How do I use Brix?

Select the °Bx scale, then set a Brix to TDS factor that matches your instrument and coffee. A warning appears if the factor is outside 0.75 to 0.95, since coffee is often near 0.85 to 0.86. Use reading correction only for small, known bias.

What does Under target mean?

Under target means either strength or extraction is below the selected target box. That often aligns with brews that taste thin, sour, or both, depending on the coffee. Common adjustments include tightening the ratio, increasing dose, or extracting more evenly through grind and time.

Can I use it offline?

Core calculations do not require network requests, but the chart view depends on a page script that may need to load unless it is already cached. Clipboard and downloads also depend on your browser permissions and settings.

How much does it cost?

This package does not include pricing or licensing terms. Availability and usage terms depend on where it is hosted and how it is offered.

Troubleshooting:

No summary appears: make sure dose, beverage mass, and strength are all above 0.
You see “Strength is zero”: confirm you entered a refractometer number and chose the correct scale.
TDS looks impossibly high: recheck whether the device reading is %TDS or °Bx.
You get a Brix warning: move the factor toward 0.85 to 0.86 unless you have a calibration.
The control chart is blank: switch to the chart view after results are present and reload if needed.
Copy buttons do nothing: check clipboard permissions in your browser and try the download option.
Downloaded chart files look blurry: prefer PNG or WebP, and avoid re-saving screenshots.

Blocking issue: If you entered values but still see “Awaiting inputs”, one of the key numbers is being treated as 0. Re-enter dose, beverage mass, and the refractometer reading with a decimal point if needed.

Advanced Tips:

Tip Use beverage mass rather than volume for repeatable comparisons across cups and temperatures.
Tip For espresso, set beverage density closer to 1.02 to 1.05 to make the mL estimate more realistic.
Tip Tune absorption ratio to match your brewer so the estimated brew water aligns with your kettle dose.
Tip If you use bypass, log both beverage ratio and water ratio to avoid confusing strength changes with extraction changes.
Tip Watch the pair of strength and extraction together, since the same extraction can taste different at different strengths.
Tip Use small, consistent recipe changes and compare exported numbers to avoid being misled by display rounding.

Glossary:

Total Dissolved Solids: Percent of beverage mass that is dissolved coffee material.
°Bx: Brix scale reading that can be converted to coffee TDS using a factor.
Extraction yield: Percent of the dry coffee dose extracted as dissolved solids.
Dissolved solids: Mass of extracted material computed from beverage mass and TDS.
Absorption ratio: Estimated water retained in the grounds per gram of coffee.
Bypass water: Water added after brewing to dilute the beverage.
Brewing control chart: Plot of extraction yield versus strength with a target box.
Beverage density: Grams per milliliter used to estimate beverage volume.