Stock & Sauce Reduction Calculator
Work out a stock or sauce reduction three ways — by a percentage, to a target volume or to a flavour strength — with the liquid to boil off, an estimated simmer time for your pan and heat, how deep the liquid should end up, the final saltiness and servings.
How it works
Final volume = start × (1 − reduce% ÷ 100) = target = start ÷ strength · Boiled off = start − final · Concentration = start ÷ final · Time ≈ boiled off ÷ evaporation rate, where rate ≈ pan area (cm²) ÷ 100 × 2, 4 or 7 ml/min (gentle simmer, steady simmer, rolling boil) · Depth = volume ÷ pan area · Final salt % = starting salt % × concentration
Reducing a liquid drives off water while the dissolved solids stay, so flavour, sugar and salt all concentrate in proportion to the volume you lose. “Reduce by half” leaves 50% and doubles the strength; reducing by 75% leaves a quarter and makes it about four times as strong. Plan it the way your recipe is written: by a percentage, down to a target volume (for example “reduce to 1 cup”) or to a strength. The calculator then estimates how long it will take from the pan’s surface area and the heat, because evaporation happens at the surface: a wide skillet at a rolling boil reduces several times faster than a narrow saucepan at a gentle simmer. It also gives the liquid depth at the start and when you are done, so you can check progress with a ruler instead of guessing, and a milestone table with the time to each 10% step. Under More options, enter the salt in your starting liquid to see how salty the result will be, and a serving size to count portions. Treat the time as a guide — lids, thick sauces and weak burners slow evaporation.
Worked example
You start with 1,000 ml of stock in a 10-inch (25 cm) pan and reduce by 60% at a steady simmer. The final volume is 1,000 × 0.40 = 400 ml, you boil off 600 ml, and the flavour is 1,000 ÷ 400 = 2.5× as concentrated. The pan’s surface is π × 12.7² ≈ 507 cm², so it evaporates about 507 ÷ 100 × 4 ≈ 20 ml a minute, and the reduction takes about 600 ÷ 20 ≈ 30 minutes. The stock starts about 2 cm deep and is done at about 0.8 cm. If it was store-bought broth at 0.9% salt, the reduced sauce would be 0.9 × 2.5 ≈ 2.3% salt — far too salty, so use unsalted stock.
Frequently asked questions
What is the difference between “reduce by half” and “reduce to half”?
They mean the same final volume — 50% remaining. “Reduce by 75%” leaves a quarter, while “reduce to a quarter” also leaves 25%. If your recipe gives the end volume instead (“reduce to 1 cup”), switch Plan by to Target volume and enter it directly.
How long does it take to reduce a sauce by half?
It depends mostly on the pan’s width and the heat. In a 10-inch pan at a steady simmer, about 20 ml evaporates each minute, so halving 1 liter takes roughly 25 minutes; a rolling boil in a 12-inch skillet can do it in about 10. Enter your pan and heat for an estimate, and check the depth as you go.
Why does my reduced sauce taste too salty?
Reduction removes water but not salt, so the salt concentrates along with the flavour. Broth that tastes right at 0.9% salt becomes over 2% when reduced by 60%. Use unsalted or low-sodium stock, season at the end, and enter the salt percentage under More options to check before you start.
Does reducing faster ruin the flavour?
A hard boil reduces quickly and is fine for stocks, wine and pan sauces. Dairy and emulsified sauces can break or catch at a rolling boil, and sugary glazes burn easily, so reduce those at a gentle simmer and stir more often near the end.
How can I tell when I have reduced enough?
Dip a clean ruler or chopstick in at the start and note the depth, then compare it with the finishing depth the calculator shows. Texture is the other cue: a coating that holds a line on the back of a spoon for sauces, or a honey-like flow for glazes, which thicken further as they cool.
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This calculator is for educational purposes. Double-check important results before acting on them.