Percent Solution Calculator

A percent solution expresses how much solute is in a fixed amount of finished solution, and the three conventions are not interchangeable. % w/v is grams of solute per 100 mL of solution, % v/v is millilitres of liquid solute per 100 mL of solution, and % w/w is grams of solute per 100 g of final batch. Enter the type, the percentage and the amount you want to make, and the calculator returns exactly how much solute to weigh or measure. Add a molecular weight to a w/v solution and it also reports the molarity.

Percentages look like the simplest concentration unit in the lab, which is exactly why they cause so many quiet errors. "5% solution" means three different things depending on whether the solute is a solid, a liquid, or mixed by weight — and a protocol that just says "5%" is asking you to guess. This calculator forces the distinction up front: choose w/v, v/v or w/w and the meaning of the number is pinned down. It sits in our laboratory calculator set and it is the natural companion to the stock solution calculator when you are scaling a recipe up or down.

The reference denominator is always 100 of the finished unit. For w/v that is 100 mL of solution, so 5% w/v is 5 g of solute brought to 100 mL — not 5 g added to 100 mL of water, which would give slightly more than 100 mL and a shade under 5%. For w/w it is 100 g of final batch, which is why weight-based recipes are made by total mass on a balance rather than by volume. When the solute is a known compound and you also need moles, the molarity calculator takes the mass and volume further.

One genuinely useful bridge is built in: for a w/v solution, if you supply the solute's molecular weight the calculator reports the molarity alongside the mass to weigh. That turns a bench-friendly "% w/v" instruction into the mol/L number a downstream calculation needs, without a second tool.

How to use the percent solution calculator

Choose the type first — w/v (mass of solid in a final volume), v/v (volume of liquid in a final volume) or w/w (mass in a final mass). This decides which amount field you fill in.

Enter the percentage you are targeting. Values above 100 are rejected for v/v and w/w because a liquid cannot be more than 100% of the volume, and flagged for w/v as implausibly concentrated.

For w/v and v/v, enter the final volume and pick its unit (mL or L). For w/w, enter the final batch mass and its unit (g or kg).

Optionally enter the molecular weight (g/mol) for a w/v solution. With it, the calculator also reports the molarity of the finished solution.

Press Calculate. The primary card is the solute to weigh or measure; the secondary cards echo the percentage, the final amount, and the molarity when you provided a molecular weight.

Percent Solution formula

% w/v: mass (g) = (% ÷ 100) × volume (mL)

% v/v: solute volume (mL) = (% ÷ 100) × final volume (mL)

% w/w: mass (g) = (% ÷ 100) × batch mass (g)

molarity (w/v) = (g ÷ L) ÷ MW

% = target percentage · volume = final solution volume · batch mass = final w/w mass · MW = solute molecular weight (g/mol). Make up to the final amount; do not add solute to a fixed volume of solvent.

Variables and units

Symbol	Meaning	Unit
%	Target percentage	%
mass	Solute mass to weigh (w/v, w/w)	g
volume	Solute or final volume (v/v, w/v)	mL
batch mass	Final w/w batch mass	g
MW	Solute molecular weight	g/mol
molarity	Molarity of a w/v solution	mol/L

How percent solution is calculated

Fix the convention: w/v uses grams per 100 mL, v/v uses mL per 100 mL, w/w uses grams per 100 g.
Convert the target amount to the reference unit — final volume to mL for w/v and v/v, final batch mass to g for w/w.
Multiply the fraction by the amount: solute = (% ÷ 100) × amount.
For a w/v solution with a molecular weight, divide grams per litre by MW to get molarity.
Weigh or measure the solute, then make up to the final volume or mass — do not add the solute to the full amount of solvent.

Worked laboratory examples

Example 1 — 250 mL of 5% w/v NaCl

Given: type w/v · 5% · final volume 250 mL

mass = (5 ÷ 100) × 250 mL = 12.5 g
weigh 12.5 g NaCl, dissolve, make up to 250 mL

Result: 12.5 g of NaCl made up to 250 mL

Example 2 — 5% w/v glucose with a molecular weight

Given: type w/v · 5% · final volume 1 L · MW 180.16 g/mol

mass = (5 ÷ 100) × 1000 mL = 50 g
g/L = 50 g ÷ 1 L = 50 g/L
molarity = 50 ÷ 180.16 ≈ 0.278 M

Result: 50 g of glucose, a 0.278 M solution

Example 3 — 500 mL of 70% v/v ethanol

Given: type v/v · 70% · final volume 500 mL

solute volume = (70 ÷ 100) × 500 mL = 350 mL
measure 350 mL of absolute ethanol, make up to 500 mL with water

Result: 350 mL of ethanol made up to 500 mL

Example 4 — 200 g of 10% w/w sucrose

Given: type w/w · 10% · final batch mass 200 g

mass = (10 ÷ 100) × 200 g = 20 g
weigh 20 g sucrose and 180 g of the remaining batch

Result: 20 g of sucrose in a 200 g batch

Want the reasoning behind the numbers? Read Percent Solutions: w/v, v/v and w/w.

How to interpret the result

The primary number is what you physically handle — grams on a balance or millilitres in a cylinder. The percentage it came from is only meaningful once you know which convention you picked, which is why the secondary card repeats it: 5% w/v and 5% w/w are different recipes for the same word.

For w/v, the optional molarity is the bridge to quantitative work. It assumes the solute mass is dissolved and made up to the stated final volume; if you instead add the solid to the full volume of solvent the real concentration will be lower, and the reported molarity will be optimistic.

A v/v or w/w percentage above 100 is rejected outright — it is physically impossible for the solute to be more than the whole. A w/v value above 100 g per 100 mL is allowed but flagged, because very few solutes are that soluble and the number is usually a units slip.

Assumptions

Percentages follow the standard conventions: w/v is g per 100 mL of solution, v/v is mL per 100 mL of solution, w/w is g per 100 g of batch.
The solute is dissolved and the solution is made up to the final volume or mass, not added to a fixed amount of solvent.
Volumes are treated as additive for w/v and v/v; for precise work make up to a volumetric mark.
The molarity bridge assumes the solute does not change the final volume beyond what you made up to.

Limitations

It does not check solubility — a percentage can be arithmetically valid for a solute that will not fully dissolve.
The v/v additive-volume assumption breaks down for mixtures like ethanol and water, which contract slightly on mixing.
No density data is used, so a w/w-to-w/v or w/v-to-w/w conversion is not offered; those need the solution density.
The molarity output is only available for w/v solutions, where a mass-per-volume figure can be turned into moles.

Common mistakes

Reading "5%" without checking whether it means w/v, v/v or w/w — the three give different amounts of solute.
Adding the solute to the full final volume of solvent instead of dissolving it and making up to the mark, which dilutes the result.
Confusing % w/v with molarity; a 1% w/v solution is 10 g/L, and its molarity depends entirely on the molecular weight.
Trying to express a v/v or w/w percentage above 100, which has no physical meaning.
Using volume for a w/w recipe or mass for a v/v recipe, because the units look interchangeable when they are not.

FAQ

What does % w/v mean?

Weight per volume: grams of solute in 100 mL of finished solution. A 5% w/v solution contains 5 g of solute made up to 100 mL. It is the usual convention for solids dissolved in a liquid.

What is the difference between w/v, v/v and w/w?

w/v is grams of solute per 100 mL of solution, v/v is millilitres of liquid solute per 100 mL of solution, and w/w is grams of solute per 100 g of final batch. The denominator — final volume versus final mass — is what separates them, and the same percentage means a different recipe under each.

How do I make 100 mL of a 10% w/v solution?

Weigh 10 g of solute, dissolve it in less than 100 mL of solvent, then make the volume up to exactly 100 mL. Do not add 10 g to 100 mL of solvent — that gives slightly more than 100 mL and a slightly weaker solution.

How do I convert a percent solution to molarity?

For a w/v solution, the percentage is 10× the grams per litre (1% w/v = 10 g/L), so molarity = (percent × 10) ÷ molecular weight. A 5% w/v glucose solution (MW 180.16) is 50 ÷ 180.16 ≈ 0.278 M. Enter the molecular weight here and the calculator does it for you.

Can a percentage be over 100?

Not for v/v or w/w — a liquid solute cannot exceed the total volume, and a mass cannot exceed the total mass, so both are rejected. A w/v figure above 100 g per 100 mL is technically possible but almost always a mistake or a solubility limit, so it is flagged.

Why is my w/w recipe measured by mass, not volume?

Because weight/weight is defined against the total mass of the batch. You weigh both the solute and the rest of the batch on a balance; volume never enters the calculation, which is why w/w is preferred when density varies with temperature or composition.

Scientific Sources

Promega Biomath — Dilution Calculator · Tier 2 source
NEB NEBioCalculator · Tier 2 source
NIST Chemistry WebBook · Tier 1 source

External links open in a new tab and carry rel="nofollow". We cite primary references (NIST, NIH/NCBI, peer-reviewed papers) and established manufacturer technical documentation (NEB, Thermo Fisher, Promega, IDT). Calculated results are estimates; your protocol and manufacturer guidance take precedence.

Last reviewed: 2026-09 · Method version: 1.0

Percent Solution Calculator