Mill certificates are almost always requested and almost never read. The sheet goes into the project file, gets signed, and stays there until the supervising consultant asks for it. Yet that single page answers the most expensive question on any site: is the steel you are about to cast into concrete really what you ordered?

This article takes a rebar mill certificate apart section by section, explains what each field means, and — more importantly — shows how to reconcile it with the delivery note and the bars stacked on your site. No metallurgical background is needed, only ten careful minutes.

What a mill certificate is, and how it differs from an SPPT-SNI

A mill certificate — also called a mill test certificate or works certificate — is a test report issued by the producing mill for a specific set of products. It is a per-batch document: it covers only the steel melted under the heat number printed on it, not the mill's entire output.

The SPPT-SNI is different. That certificate states that the mill and its product type are entitled to carry the SNI mark, and it is valid for a period rather than for one shipment. The two complement each other and should both be requested: the SPPT-SNI once at the start of the relationship, the mill certificate with every delivery.

A third document is often confused with these: independent laboratory test results commissioned by the project owner. Those test samples you selected yourself, which makes them a cross-check rather than a replacement for the mill certificate.

Reading a mill certificate line by line

The identity block

The header carries the mill's name and address, the document number, and the issue date. Confirm that the mill named there is the same one your distributor told you about. If your distributor names one mill and the document shows another, that is not an administrative detail to wave away.

Heat number

This is the key to traceability. A heat is one melting of steel, and every test result on the document refers to that heat. The same number should appear on the tags of the bundles delivered. If the delivery note lists three heats, there should be three sets of results or three documents.

Product description

States the type (plain or deformed), nominal diameter, bar length, and grade. Check all three against your order. The number in the grade denotes nominal yield strength in MPa: BjTS 420 means deformed rebar with a nominal yield strength of 420 MPa, and BjTP 280 means plain bar at 280 MPa.

Mechanical test results

The core of the document, normally covering yield strength, tensile strength, elongation, and the bend test. What you need to do is simple: confirm that every reported value sits above the minimum requirement for the ordered grade shown in the adjacent column, and that the bend test column reads pass rather than being blank. A properly issued certificate prints the requirement next to the result so the comparison needs no standards book.

Chemical composition

Usually carbon, manganese, silicon, phosphorus, sulphur, and the carbon equivalent value. For a contractor, the carbon equivalent is the most relevant column, because it relates to how readily the steel can be welded. If your works involve welding reinforcement, ask for this figure at quotation stage, not after delivery.

Standard reference and signature

The footer names the testing standard — for rebar in Indonesia that is SNI 2052 — along with the name and signature of the person responsible for quality. A sheet with no standard reference and no responsible signatory does not deserve to be called a mill certificate.

The standard weight table for matching paperwork to steel

A mill certificate speaks to quality, not to the quantity and size that actually arrived. That calls for a weight check. Rebar weight follows the SNI formula and depends on diameter alone: weight (kg/m) = 0.006165 × d², with a standard bar length of 12 metres. Plain and deformed bars of the same diameter weigh exactly the same.

Diameter Weight per metre Weight per bar (12 m) Weight of 100 bars
8 mm 0.395 kg 4.73 kg 473.5 kg
10 mm 0.617 kg 7.40 kg 739.8 kg
12 mm 0.888 kg 10.65 kg 1,065.3 kg
13 mm 1.042 kg 12.50 kg 1,250.3 kg
16 mm 1.578 kg 18.94 kg 1,893.9 kg
19 mm 2.226 kg 26.71 kg 2,670.7 kg
22 mm 2.984 kg 35.81 kg 3,580.6 kg
25 mm 3.853 kg 46.24 kg 4,623.8 kg
32 mm 6.313 kg 75.76 kg 7,575.6 kg

The last column is included because rebar arrives in bundles, and weighing one whole bundle is far quicker than weighing bars one at a time.

A ten-minute reconciliation example

Suppose the delivery note lists 200 bars of D16 from a single heat, with a shipped weight of 3,788 kg. From the table, one D16 bar weighs 18.94 kg, so the expected weight is 200 × 18.94 = 3,788 kg. The figures agree, which means size and count are consistent.

Now take a second case: the paperwork again says 200 bars of D16, but the weighbridge reads only 3,410 kg. The shortfall is 3,788 − 3,410 = 378 kg, roughly 10 percent below standard. A gap that size cannot be explained by rounding; the actual diameter is what needs checking.

To confirm, take one bar, measure its length, and weigh it. If a 12-metre bar reads about 17.0 kg, its weight per metre is 17.0 ÷ 12 = 1.417 kg/m, while D16 should be 1.578 kg/m. A difference of that order points to an effective diameter below nominal, and the accompanying mill certificate does not describe what you actually received. Undersized bar and how to spot it is covered further in our SNI rebar guide.

The four most common mistakes

Accepting a document without matching the heat number

A certificate from another batch still looks convincing because the format is identical. The heat number on the document must also appear on the tags of the bundles delivered.

Treating the SPPT-SNI as sufficient

The SPPT-SNI says the mill is entitled to use the SNI mark, not that today's shipment passed its tests. The two answer different questions.

Reading results without the requirement column

A high yield figure means nothing if the grade tested differs from the grade ordered. Always read result and requirement as a pair.

Filing documents without tying them to a pour

When a quality doubt arises later, what matters is the steel in one particular structural element. Record which heat went into which pour; that simple habit saves a great deal of time when an audit arrives.

Frequently Asked Questions

Is every delivery entitled to a mill certificate?

For project purchases, yes. The document is issued by the mill per batch and should be passed on unchanged by the distributor. If a supplier says none is available, that answer deserves questioning before the next order is placed.

Is a copy or a scan good enough?

For routine checking it usually is, as long as every field is legible and the heat number can be matched against the bundle tags. If your contract requires originals, say so at the outset so the mill and distributor can prepare them.

What if a test result sits right at the requirement?

A value that meets the requirement passes. That said, on critical works it is normal and sensible to take samples for testing at an independent laboratory.

Which grades are available and where are the details?

Diameters, grades and bar lengths are listed on the Product Specification page. Available grades include BjTP 280 for plain bar and BjTS 420 and BjTS 550 for deformed bar. Certification evidence is shown on the Certification page.

Can I ask for a sample mill certificate before ordering?

You can, and you should. A certificate from an earlier shipment shows the format, how complete the fields are, and how the mill reports its results. Ask for one together with your request for quotation.

Next step

A mill certificate is only useful once it is read and reconciled. Three habits close most of the risk: match the heat number to the bundle tags, read results paired with their requirement column, and weigh one bundle to confirm the size that arrived matches the paperwork.

Inter World Steel is a steel mill in Tangerang with more than 50 years of experience, producing plain and deformed rebar certified to SNI 2052:2024, with SPPT-SNI and mill certificates issued per batch. For project requirements, send your size list and volumes through the Order Now page, or contact the sales team via the Contact page to check stock, request a quotation, and ask for sample quality documents. If you are still shortlisting suppliers, the full set of considerations is on the guide to choosing a rebar distributor page.