ASTM D1209 · D1544 · D156

Color scale converter (APHA, Pt-Co, Hazen, Gardner, Saybolt)

Settle whether the COA color meets your spec before the drums ship.

Enter the color reading from the COA and, if you like, the limit from your spec. The tool shows the reading on each scale only as far as published sources allow, and says so when only a retest can answer.

Last updated 2026-09-28. Math runs in your browser, no data leaves your computer.

Chinese factories usually report color in Hazen, while a US or Australian spec for the same product may say APHA, Gardner or Saybolt. The first case is easy, because APHA, Pt-Co and Hazen are one scale under three names.

The other cases are not, and nobody publishes a clean table between them. This tool uses only the anchors that instrument makers publish, so an answer of "cannot tell" is the honest one and the fix is a retest on your scale.

Read the unit next to the color line on the COA, since the same number means very different things on Gardner and on APHA.

Type the number as printed, so a Hazen reading of "≤10" goes in as 10 and the tool treats it as the worst case.

A Saybolt limit is a minimum because a higher Saybolt number is a clearer product, which is the reverse of the other two scales.

Take it from your purchase spec or the TDS the price was agreed on, because that is the document a rejection has to rest on.

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.

What the placement rests on

APHA, Pt-Co and Hazen are one platinum cobalt scale running from 0 to 500, so the tool copies the number across unchanged. The visual method is ASTM D1209, and the instrumental method ASTM D5386 covers readings from 0 to 100.

Between APHA and Gardner there is one published anchor. HunterLab (posted 10 January 2023) says an APHA 500 standard is just under Gardner 2, and Konica Minolta puts APHA 500 at roughly Gardner 2 to 3. Any APHA reading therefore sits below Gardner 3 on both sources and below Gardner 2 on HunterLab's, a Gardner reading under 2 sits inside the APHA range at a value nobody publishes, and from Gardner 3 up the color is beyond APHA 500. The tool uses the stricter of the two sources whenever it decides a spec question.

Gardner is defined by 18 glass standards in ASTM D1544, with an instrumental version for pine chemicals in ASTM D6166. Saybolt runs from +30 to −16 under ASTM D156, and ASTM D6045 reads the same scale by instrument, as the optek overview also sets out. No public source ties Saybolt to APHA or Gardner, so the tool never crosses that line.

Worked example. A resin spec written in Gardner

The booking. A coatings plant buys a hydrocarbon resin solution on a spec of Gardner 2 maximum, and the factory COA reads Hazen 400. Hazen 400 is the same as APHA 400, and APHA 500 is just under Gardner 2 on the HunterLab anchor, which looks fine on paper.

The failure. Konica Minolta puts the same APHA 500 at Gardner 2 to 3, so the two published sources do not agree on where the scales cross, and Gardner 2 sits right in the gap. A conversion cannot prove the lot meets a Gardner 2 limit, and if the resin comes in dark the COA gives the buyer no grounds to reject it. The choice is simple: accept the lot on trust, or get the reading on the scale the spec names.

The fix. The buyer asks the factory to test the retained sample to ASTM D1544 before loading. The lab reports Gardner 1, which is under the Gardner 2 limit on the spec's own scale, and the lot ships with a COA that answers the spec directly.

Writing the COA requirements into the purchase order? The COA template lays out the test, method, limit and result lines, so the color line names its scale and method from the start.

Frequently asked

Are APHA, Pt-Co and Hazen the same scale?

Yes, they are three names for one platinum cobalt scale that runs from 0 for distilled water to 500 for a pale yellow, as both HunterLab and Konica Minolta describe it. A COA that reads Hazen 20 and a spec that says APHA 20 maximum are talking about the same number. The visual method is ASTM D1209, and a Chinese COA often prints it as 色度 with the unit Hazen or 铂-钴.

How do I convert Gardner color to APHA?

You can only place it roughly, because no public point by point table exists and the scales are not linear. The published anchor is the top of the APHA scale: HunterLab says an APHA 500 standard is just under Gardner 2, and Konica Minolta says APHA 500 is roughly Gardner 2 to 3. So a Gardner 1 sits somewhere inside the APHA range, and anything from Gardner 3 up is past the end of the APHA scale.

Can Saybolt color be converted to APHA or Gardner?

Not from any published table this tool could cite. Saybolt under ASTM D156 runs from +30 for the clearest refined oils down to −16, and ASTM D1500 takes over for darker products. Where a spec is written in Saybolt and the COA in APHA, ask the supplier to test a retained sample in Saybolt.

Which color scale is normal for which product?

APHA, Pt-Co or Hazen for near colorless liquids such as solvents, alcohols and petroleum distillates. Gardner for yellow to brown liquids such as resins, fatty acids, drying oils, varnishes and tall oil products. Saybolt for refined petroleum products such as kerosine, naphthas, jet fuel and white oils. A spec should name both the scale and the test method, so the lab and the buyer measure the same way.

Why does the tool refuse to give a single converted number?

Because the sources do not support one, and a made up number on a COA dispute helps nobody. The Gardner scale changes hue as well as depth, running from a red yellow to a green yellow over its 18 steps according to HunterLab, so any single conversion factor would be wrong somewhere. The tool gives the range the published anchors support and tells you when only a retest can settle it.

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Sourzi shows what official files say. It is not customs or legal advice. For a binding answer, ask a licensed customs broker, a CBP ruling or an Australian Border Force Tariff Advice.

File dates and links are on Data sources.