Measuring Extraction Yield: TDS, Refractometers, and the SCA Range

5 min read · Updated June 10, 2026

How to measure coffee extraction yield with a refractometer: the TDS formula for filter and espresso, what the SCA 18–22% range means, and how to use the numbers to brew better.

If you log your brews, sooner or later you want a number that says how a cup actually went, beyond “pretty good, I think.” Extraction yield is that number. It tells you what percentage of the dry coffee dissolved into the cup, and it turns vague impressions like “stronger” or “more bitter” into something you can track across brews, coffees, and months.

This guide covers what TDS and extraction yield mean, the formula, how to take a clean refractometer reading, and what to do with the numbers once you have them.

Strength and extraction are two different numbers

TDS (total dissolved solids) is the concentration of the drink in your cup, measured as a percentage. Filter coffee typically reads 1.15–1.45%; espresso reads 8–12%. TDS is what your tongue perceives as strength or body.

Extraction yield is the percentage of the dry grounds that dissolved. Coffee is only about 30% soluble at the extreme, and most balanced brews dissolve 18–22% of the dose. Yield is what your tongue perceives as the balance moving from sour (low) through sweet to bitter and dry (high).

The two are independent. A ristretto can be very strong at a low yield. A long, slow brew can be weak in the cup yet over-extracted. Strength is adjusted with the brew ratio; extraction is adjusted with grind, temperature, time, and technique. Keeping the two ideas separate is the single biggest payoff of measuring at all.

The formula

Extraction yield % = beverage weight (g) × TDS (%) ÷ dose (g)

Three numbers, two of which you already log:

• Dose: the dry coffee weight, e.g. 18g.
• Beverage weight: what actually ends up in the cup. Weigh the vessel before and after, or subtract retained water (about 2g per gram of coffee) from your pour weight if you skip the cup weigh. For espresso, beverage weight is simply the shot weight you stopped at.
• TDS: the refractometer reading.

Example: 18g dose, 250g of water poured, 214g in the cup, TDS reads 1.38%. 214 × 1.38 ÷ 18 = 16.4%. That cup is likely on the sour, underdeveloped side, and the number agrees with what the palate usually reports at that yield.

BeanBench does this math for you: enter the TDS reading on any brew log (and the cup weight if you measured it) and the app computes the yield and flags where it sits relative to the SCA range. Over time the Analytics tab reports your average yield and how many of your measured brews land inside 18–22%.

What the SCA range actually claims

The Specialty Coffee Association’s Golden Cup standard recommends brews in the 18–22% extraction band at roughly 1.15–1.45% TDS. It descends from Ernest Lockhart’s Coffee Brewing Institute work in the 1950s, which surveyed what drinkers preferred and drew a target box around it.

Treat the box as a reference, with two caveats. First, it was built around drip coffee and average preferences from decades ago; modern light roasts brewed with soft water often taste clean and sweet at 22–23%. Second, an in-range number does not guarantee an even extraction. A channeled brew can average 20% while combining over- and under-extracted regions that taste muddled. The number summarizes the cup; it cannot certify it.

Taking a reading worth trusting

Refractometers (the VST LAB Coffee III and Atago PAL-COFFEE are the two common choices) read how much light bends through a sample, which tracks dissolved solids. The meter is the easy part. The sample is where readings go wrong:

1. Stir the brew first. The bottom of a pour-over carafe is more concentrated than the top.
2. Let the sample cool. Most meters correct for temperature, but a near-boiling drop on a room-temperature lens reads unstably. A minute or two is enough.
3. Rinse and dry the lens between readings. Residue from the last sample skews the next.
4. Take two readings. If they disagree by more than ~0.05% TDS on filter coffee, resample.
5. For espresso, consider filtering the sample. Suspended fines and oils read as dissolved solids on some meters; a syringe filter improves repeatability.

Using the numbers

A single reading is trivia. The value shows up when you log yields next to the variables you changed:

• Dialing a new coffee. If the first cup reads 17% and tastes sharp, you know the size of the move: grind meaningfully finer rather than nudging by half a step.
• Testing a change honestly. Swapped filters, raised the temperature, tried a new pour pattern? The yield tells you whether extraction actually moved or you imagined it.
• Finding your own band. After a dozen measured brews, your ratings start to cluster. Plenty of people discover their favorite cups sit at 19–20% for naturals and 21–22% for washed coffees. That personal band is more useful than any published standard.
• Diagnosing drift. If yields slide downward over weeks at the same settings, suspect burr wear or aging beans before you blame your technique.

Export helps here too: BeanBench’s CSV and JSON exports include dose, beverage weight, TDS, and computed yield for every measured brew, so you can run your own analysis in a spreadsheet or notebook.

If you skip the meter

A refractometer is a tool for comparing brews, and around $700 for the VST (the Atago is less). Skipping it is a reasonable choice. You can still apply the framework: weigh your beverage, keep your ratio fixed, change one variable at a time, and score the cup. The yield number makes the feedback loop faster and more honest, but the loop itself is the thing that improves your coffee.