Solvent Evaporation & Concentration Increase Calculator
Find the new concentration after solvent evaporates, work out how much solvent to remove for a target concentration or mass percent, and estimate the evaporation time, all with step-by-step working.
Pick a calculation, enter the known values, and optionally add an evaporation rate to estimate the time needed.
New concentration (C₂)
Formula used: C₂ = C₁ × V₁ ÷ V₂ (V₂ = V₁ − evaporated volume)
400 mL
Remaining volume
1.25×
Concentration factor
20%
Volume reduction
—
Estimated time
Volume Loss & Concentration Increase Visual
The same amount of solute (dots), packed into a shrinking volume as solvent evaporates away.
Step-by-Step Evaporation Calculation
Here's exactly how this answer was calculated, one step at a time.
Given: C₁ = 1 mol/L, V₁ = 500 mL, evaporated = 100 mL
Step 1: Find the remaining solvent volume
Evaporation removes solvent only — the solute stays behind, so the total volume simply shrinks by whatever left as vapor.
V₂ = V₁ − evaporated volume = 500 − 100 = 400 mLStep 2: Apply C₁V₁ = C₂V₂ (moles of solute don't change)
Because the amount of solute is fixed, cramming it into a smaller volume raises the concentration in direct proportion.
C₂ = C₁ × V₁ ÷ V₂ = 1 × 500 ÷ 400 = 1.25 mol/LStep 3: Report the result
New concentration (C₂) = 1.25 mol/L (concentration factor 1.25×)
Calculated result:
1.25 mol/L
Solvent Evaporation & Concentration Increase Calculator: Concentrate Any Solution Online
This free solvent evaporation calculator tells you exactly what happens to a solution's concentration when some of the solvent is boiled off, air-dried, or otherwise removed. Type in what you already know — a starting concentration, a starting volume or mass, and how much solvent is leaving — and it works out the new concentration instantly, with every step of the math shown.
It also runs the other way around. If you already know the concentration you're aiming for, the calculator tells you exactly how much solvent needs to evaporate to get there, whether you're working in molarity, a general concentration unit, or a mass percent (% w/w) figure. Add an evaporation rate and it will even estimate how long the process should take.
What Happens When a Solvent Evaporates?
When a solvent evaporates from a solution, it leaves as vapor and takes none of the dissolved solute with it. That's the whole idea behind evaporation as a concentrating step: the solute — salt, sugar, a dissolved drug, a flavor compound, anything that isn't volatile enough to leave with the vapor — stays behind in a shrinking pool of liquid.
Since the same amount of solute is now dissolved in less liquid, its concentration goes up. This is true whether you're thinking in terms of molarity (moles per litre), a mass-based percent (grams of solute per hundred grams of solution), or almost any other way of expressing concentration. The chemistry is simple, but getting the numbers right by hand can be fiddly — this calculator does the arithmetic for you and shows the working alongside it.
The Simple Math Behind Concentration Increase (C1V1 = C2V2)
The volume-based side of this calculator uses the same equation as a dilution calculation, just run in reverse. Because the moles of solute don't change, C1 × V1 (the starting concentration times the starting volume) always equals C2 × V2 (the new concentration times the new, smaller volume). Dilution adds solvent and lowers concentration; evaporation removes solvent and raises it — same equation, opposite direction.
That means if you know any three of the four values — starting concentration, starting volume, evaporated volume (which gives the new volume), and new concentration — the calculator can solve for whichever one is missing. Most people either want to know the resulting concentration after a known amount of evaporation, or the amount of evaporation needed to reach a target concentration, so those are the two volume-based modes built into this tool.
Method 1: Finding the New Concentration After Evaporation
Pick this mode when you already know how much solvent left the container — maybe you weighed or measured the solution before and after, or a recipe or lab protocol tells you to boil it down by a certain volume. Enter the starting concentration, the starting volume, and the volume that evaporated, and the calculator finds the remaining volume and the new, higher concentration.
As a worked example, starting with 500 mL of a 1 mol/L solution and evaporating off 100 mL leaves 400 mL behind. Since the moles of solute are unchanged, the new concentration is 1 × 500 ÷ 400 = 1.25 mol/L — a 1.25× increase, even though only a fifth of the volume was removed. The calculator also reports this concentration factor and the percentage the volume dropped by, so it's easy to see how proportional the two effects are.
Method 2: How Much Solvent to Evaporate for a Target Concentration
This mode flips the question around: given a starting concentration and volume, how much solvent needs to be driven off to reach a specific target concentration? Enter the starting values and the concentration you're aiming for, and the calculator works out the final volume and, from that, exactly how much solvent has to leave.
This is the more common real-world question in a lab or kitchen setting, since the target concentration is usually the thing decided in advance — a recipe calls for a syrup at a certain strength, or a protocol specifies a stock solution concentration — and the amount of boiling or air-drying needed is the unknown. The target concentration must be higher than the starting one, since evaporation can only concentrate a solution, never dilute it.
Working With Mass Percent (% w/w) Instead of Molarity
Not every situation is measured in molarity. Food and beverage concentration — reducing a sauce, making a fruit juice concentrate, boiling down a sugar syrup — almost always works in mass percent (% w/w), the grams of solute per hundred grams of total solution. The same underlying idea applies: the mass of dissolved solids doesn't change as water evaporates, so the percentage climbs as the total mass shrinks.
The two mass-based modes on this calculator mirror the volume-based ones. Enter a starting solution mass and its starting percent, then either the mass of solvent that evaporated (to find the new percent) or a target percent (to find how much solvent needs to evaporate to reach it). As a quick example, boiling 1000 g of a 10% sugar solution down until 300 g of water has evaporated leaves 700 g of solution containing the same 100 g of sugar — a new concentration of 100 ÷ 700 × 100 ≈ 14.3%.
Estimating Evaporation Time From a Known Rate
Every mode on this calculator has an optional evaporation-rate field. If you know (or have measured) roughly how fast your setup removes solvent — say, from a rotary evaporator's typical output, a simmering pot's water loss per hour, or a fume hood's air-drying rate — enter it, and the calculator divides the volume or mass that needs to evaporate by that rate to estimate how long the process will take.
This is only ever an estimate, since real evaporation rates change as a solution heats up, cools down, gets more concentrated, or as surface area and airflow shift, but it's a genuinely useful planning number for deciding whether a reduction will take twenty minutes or three hours. Leave the rate field blank if you don't have one, and every other part of the calculation still works normally.
Where Solvent Evaporation Calculations Are Used
Chemistry and biology labs use evaporation constantly to concentrate a dilute sample, remove excess solvent after an extraction, or bring a stock solution up to a usable strength — rotary evaporators, heating blocks, and simple open-air evaporation are all common ways of doing it, and this calculator's molarity-based modes cover exactly that use case.
Outside the lab, the same math shows up anywhere a liquid is deliberately reduced: cooking down a stock or sauce, concentrating fruit juice, making maple syrup from sap, brewing and distilling, drying out a paint or coating to a target solids content, and industrial processes like desalination or wastewater treatment that rely on evaporating water to concentrate whatever is left behind. Anywhere a percentage or a molarity needs to go up by removing liquid rather than adding solute, this calculator's math applies.
Mistakes to Avoid When Concentrating a Solution
The most common mixup is treating the evaporated amount as a percentage without checking whether it applies to volume or mass — a 20% volume reduction and a 20% mass reduction aren't always the same thing, especially for solutions with a density noticeably different from the pure solvent. Pick the mode (volume-based or mass-based) that matches how you actually measured the change.
It's also worth remembering that evaporation only concentrates the non-volatile solute — if the solute itself is volatile, or if there's a co-solvent that evaporates at a different rate than the main solvent, the simple C1V1 = C2V2 and mass-percent equations stop being accurate, and some solute may be lost along with the vapor. For everyday non-volatile solutes (salts, sugars, most dissolved solids), the assumption holds well; for volatile actives or fragrances, treat the result as an approximation and verify with a direct measurement.
Solvent Evaporation Calculator FAQ and Quick Reference
To find the new concentration after evaporation, use C2 = C1 × V1 ÷ V2, where V2 is the starting volume minus the evaporated volume. To find how much needs to evaporate for a target concentration, rearrange to V2 = C1 × V1 ÷ C2, then subtract V2 from V1. For mass percent, the solute mass (m1 × P1 ÷ 100) never changes, so the new percent is simply that solute mass divided by the new, smaller total mass.
This free solvent evaporation and concentration increase calculator is meant for study, lab planning, food and beverage reduction, and general reference use. It assumes the solute itself doesn't evaporate — for volatile solutes or mixed solvent systems, treat the numbers as a helpful estimate and confirm the final concentration with a direct measurement wherever accuracy really matters.
Frequently Asked Questions
Why does concentration increase when a solvent evaporates?
Evaporation removes solvent molecules only — the dissolved solute is left behind. With the same amount of solute now dissolved in a smaller volume or mass of liquid, its concentration (however it's measured) goes up.
What formula do I use to find concentration after evaporation?
Use C1V1 = C2V2, the same equation as dilution but solved in the opposite direction: C2 = C1 × V1 ÷ V2, where V2 is the starting volume minus whatever volume evaporated.
How do I find how much solvent to evaporate for a target concentration?
Rearrange C1V1 = C2V2 to solve for the final volume: V2 = C1 × V1 ÷ C2. Subtract that from the starting volume V1 to get the volume that needs to evaporate.
Does this work for mass percent (% w/w), not just molarity?
Yes. Since the mass of solute stays fixed during evaporation, the new mass percent equals the solute mass divided by the new, smaller total solution mass, multiplied by 100. This calculator has dedicated modes for exactly that calculation.
Can I estimate how long evaporation will take?
Yes — enter an evaporation rate (like mL per hour or grams per hour) in the optional rate field, and the calculator divides the volume or mass that needs to evaporate by that rate to give a rough time estimate.
Does evaporation work for volatile solutes?
The C1V1 = C2V2 and mass-percent equations assume the solute itself doesn't evaporate. For volatile solutes, fragrances, or mixed-solvent systems, some solute may leave with the vapor, so treat the calculated result as an approximation rather than an exact figure.
What's the difference between this and a dilution calculator?
A dilution calculator adds solvent to lower concentration; this calculator removes solvent to raise it. Both use the same underlying C1V1 = C2V2 relationship, just applied in opposite directions.
Can I use this for concentrating juice, syrup, or sauce?
Yes — the mass-percent modes are exactly the calculation used to figure out how much water needs to boil off a syrup, sauce, or juice to reach a target strength, since food concentration is almost always tracked by mass percent rather than molarity.