Blending · Alligation

Blending calculator for mixing two concentrations

Hit the target strength on the first blend, not the third.

Enter two strengths, the target and the batch size, and get how much of each to mix by weight or by volume.

Last updated 2026-09-27. Math runs in your browser, no data leaves your computer.

Enter the two streams you are mixing and the strength you need at the end. For a straight dilution, the weaker stream is water at 0%, and the tool treats it like any other stock.

Match the basis your strengths are quoted in, because a % w/w blend metered by volume misses the target.

The unit only labels the answer, since the ratio is the same whether you blend in kilograms, pounds, liters or gallons.

Take the assay from the certificate of analysis for the lot, because the nominal grade on the label is usually a range.

Type 0 when the second stream is water, or the assay of the weaker lot when you are blending two grades together.

The target has to sit between the two stream strengths, since no mix of two streams can land outside them.

Pick the amount of stream A when a part drum or a tank heel sets the batch, and the tool sizes stream B around it.

Leave room in the vessel for the whole blend, because the total is always larger than the amount of stream A you start with.

Before the booking, screen the name on the invoice. Shipment pre-check is on the paid plans, from USD 59 a month.

General guidance only. Verify against the cited primary sources before you commit to a shipment, declaration, or contract.

How the alligation math works

A blend that misses strength is expensive in a quiet way. The tank has to be topped up with more concentrate or more water, the assay is repeated, and the batch often grows past the size the customer ordered, which leaves an odd part tote on the floor that someone has to sell or dispose of.

The tool balances the active ingredient on both sides of the mix. The share of stream A in the finished batch is (target minus B) divided by (A minus B), and stream B makes up the rest. As a check, the tool multiplies each stream by its strength, adds them, and divides by the total to confirm the blend lands on the target.

The math is exact on a weight basis for percent w/w strengths. On a volume basis it assumes the volumes simply add, which is close for similar liquids but not exact for water with alcohols or with strong acids, so treat a volume blend as a first pass and confirm it with a density or refractive index reading before release.

Worked example: 50% concentrate down to 20%

The booking. A customer orders 1,000 kg of a 20% w/w solution, and the plant has 50% concentrate and process water. The supervisor sketches the alligation cross on a whiteboard, gets 20 and 30 on the diagonals, and writes up a batch sheet that looks fine on paper.

The failure. The numbers on the sheet are swapped, so the operator charges 600 kg of concentrate and 400 kg of water, and the batch comes out at 600 x 0.50 / 1,000 = 30% w/w. Now the choice is to add another 500 kg of water and hold 1,500 kg of product for a 1,000 kg order, or to pump part of the batch back and start again.

The fix. Run the same inputs through the tool and it returns 40% of the batch as concentrate, so 400 kg of 50% and 600 kg of water. The check reads 400 x 0.50 / 1,000 = 20% w/w, the batch weighs exactly what the order says, and the drum labels match the certificate.

Need the strength in moles per liter for a lab method rather than a percent? The molarity calculator converts percent w/w to molarity with the density from the SDS.

Blending in a tank and reading the level with a dipstick? The tank volume calculator turns a liquid height into gallons or liters for vertical and horizontal tanks.

Frequently asked

What is the alligation method for mixing two concentrations?

Alligation is a mass balance on the active ingredient. The parts of the stronger stock equal the target minus the weaker strength, and the parts of the weaker stock equal the stronger strength minus the target. To take 50% stock down to 20% with water at 0%, that is 20 parts stock to 30 parts water, or 40% of the batch as stock.

Should I blend by weight or by volume?

Blend on the same basis the strengths are quoted in. Percent w/w strengths balance exactly when you weigh both streams, while metering them in liters or gallons skews the result because a liter of a strong liquor weighs more than a liter of water. Percent v/v strengths can be metered by volume, but water and alcohols shrink slightly when mixed, so check the blend with a hydrometer or refractometer.

Why does the calculator refuse my target strength?

A blend of two streams can only land between their two strengths. Mixing 32% and 20% material can never give 35%, so the tool stops and asks you to change one of the inputs instead of returning a negative quantity.

Can I use this for dilution with water?

Yes, enter water as the weaker strength at 0%. The tool then returns the amount of concentrate and the amount of water, and for acids the rule is always to add the acid to the water, because pouring water onto concentrated acid can boil and spit.

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