Yes—90% formic acid is cheaper per tonne of active acid when its delivered price is less than about 5.88% above the delivered price of 85%. If the premium exceeds that threshold, 85% supplies the acid itself at a lower cost. This comparison assumes both concentrations are stated by mass and both grades meet the same process requirements.

For purchasing teams, that provides a useful first decision rule. Formic acid 90% contains more active acid in each tonne shipped, but the saving depends on the quoted price, delivery basis, actual assay, and cost of using it. A small advantage on the purchase calculation can disappear if switching grades creates additional handling costs or affects production.

The break-even premium is 5.88%, not 5%

The comparable unit is the cost per tonne of pure formic acid equivalent. Calculate it by dividing the delivered price per tonne of solution by the acid mass fraction:

Active-acid cost = delivered solution price ÷ acid mass fraction

For 85%, divide by 0.85. For 90%, divide by 0.90. The concentrations differ by five percentage points, but the relative increase in acid content is 90 ÷ 85 − 1, or approximately 5.88%. That is the maximum price premium 90% can carry before the two grades have equal active-acid costs.

Expressed as a purchasing threshold:

Break-even delivered price for 90% = delivered price for 85% × 90 ÷ 85

Consider an illustrative quotation of $600 per tonne delivered for 85% formic acid. Its active-acid cost is $600 ÷ 0.85, or $705.88 per tonne. The equivalent break-even quotation for 90% is $635.29 per tonne delivered.

• At $625 per tonne delivered, 90% costs $694.44 per tonne of active acid, approximately 1.62% less than the 85% option.
• At $635.29 per tonne delivered, the grades have effectively the same active-acid cost.
• At $650 per tonne delivered, 90% costs $722.22 per tonne of active acid, approximately 2.31% more than the 85% option.

These are calculation examples, not market quotations. They show why a higher invoice price can still represent better value—and why choosing the higher concentration automatically can also increase cost.

Use delivered prices on the same basis

The threshold works only when the quotations cover comparable costs. An ex-works offer for 90% cannot be compared directly with a delivered offer for 85%. Bring both to the receiving site, using the same treatment of transport, packaging, insurance, unloading, and any applicable import costs. Treat recoverable taxes consistently.

Check whether the price applies to net solution weight or another commercial basis. Drum deposits, container returns, minimum shipment sizes, and residual material left in packaging can affect the amount paid for usable acid. When those costs are material, calculate the total acquisition cost for the shipment and divide it by the active acid expected to be received.

Higher concentration reduces the solution mass required. To obtain one tonne of active acid, a buyer needs approximately 1.1765 tonnes of 85% solution or 1.1111 tonnes of 90% solution. The difference is about 65.4 kg, equivalent to a 5.56% reduction in solution mass relative to the 85% requirement.

That reduction can lower freight expenditure where charges follow shipment weight and load planning allows the saving to be captured. A fixed truck charge, minimum freight charge, or standard drum order may produce little immediate saving. Calculate the freight difference using the actual shipment arrangement rather than assuming transport costs fall by the same percentage as solution mass.

A delivered quotation already includes the freight covered by that quotation. Adding a separate theoretical freight saving would count the benefit twice. Storage comparisons also need care: fewer tonnes of solution do not establish the exact reduction in tank volume. Use the supplier’s density information at the relevant temperature for volume-based planning.

Check whether less water has value in the process

For salt production using formic acid as a reactant, the amount of active acid required depends on the reaction and production target. Increasing feed concentration does not, by itself, reduce the theoretical acid requirement. It changes how much solution—and how much water—enters with that acid.

Assuming the non-acid balance is water, 85% solution introduces approximately 176.5 kg of water per tonne of active acid. The corresponding figure for 90% is approximately 111.1 kg. The difference is again about 65.4 kg.

This can have value when the process must remove water to reach a required concentration or produce a dry salt. Lower water input may reduce part of the evaporation duty or relieve a capacity constraint. However, the monetary benefit depends on the plant’s energy cost, equipment performance, other water inputs, and operating limits. The concentration difference alone cannot establish an energy saving.

If the production recipe requires dilution to a fixed feed concentration, the plant may simply add back the water avoided during transport. In that case, the commercial benefit may come mainly from buying and moving less solution. Allow for any additional dilution work, metering changes, or equipment requirements before treating the calculated saving as a net benefit.

A change in concentration also changes the acid delivered by a fixed mass or volume dose. Production should review dosing settings and the heat released during dilution or reaction. Purchasing can use the price calculation to identify an attractive offer, but process approval determines whether the grade can deliver that value.

Quality remains part of the comparison. Two grades with different impurity profiles may behave differently in a process even when their active-acid costs are equal. For a salt product with defined purity, colour, or downstream performance requirements, compare the relevant specifications alongside concentration. A lower acid cost offers little advantage if it increases rework or causes rejected output.

Turn the calculation into an order decision

Use the contractual assay basis consistently. A nominal grade name may describe a target concentration, a minimum guarantee, or a specification range. Comparing one supplier’s typical assay with another supplier’s guaranteed minimum can make the first offer appear better than the contract actually supports.

For bid evaluation, the guaranteed concentration provides a defensible starting point. Batch certificates can support receipt checks and subsequent cost reconciliation. If payment is adjusted for assay, use the agreed adjustment method. A reported concentration only helps the calculation when its measurement basis and acceptance terms are clear.

Before awarding the order, resolve four questions:

• What is each grade’s delivered cost per tonne of active acid on a consistent contractual basis?
• How much of the lower shipment mass produces a measurable freight, packaging, or inventory saving?
• Does the lower water input reduce process cost, or will water be added back?
• Do quality, dosing, storage, and handling requirements introduce costs that change the ranking?

Where those differences can be quantified, extend the comparison to cost per tonne of usable active acid: acquisition cost plus relevant grade-specific operating costs, divided by the usable acid quantity. Include demonstrated losses or yield effects; avoid assigning speculative savings merely because one grade is more concentrated.

If the delivered premium for 90% is comfortably below 5.88% and both grades are technically acceptable, the active-acid calculation supports buying 90%. A premium above that level needs a measurable process or logistics benefit to justify it. When the offers sit close to break-even, assay guarantees, shipment charges, and the plant’s water balance deserve more attention than the concentration printed on the quotation.