Marble Block : Measurement, Grading and Slab Yield
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Marble Block Buying Guide: Measurement, Grading and Slab Yield
We have already described how we handle marble block trading: enquiry, source verification, block review, commercial offer, pre-shipment inspection, payment, loading and documents. That article covers the process.
This one covers the arithmetic that determines a block buyer's cost. Disputes in block trade often centre on three questions:
Who measured the block, and on what basis was the invoiced volume calculated?
What exactly does "first quality" mean in this contract?
How many saleable m² of slabs will the invoiced m³ produce in my plant?
Putting these three in writing before contracting reduces ambiguity and later disputes.
1. On what basis is block volume measured?
A natural block is not a regular prism, so volume is derived from reference dimensions rather than from the block's true geometry. The reference standard for rough blocks is EN 1467 (Natural stone — Rough blocks — Requirements), which defines three relevant geometric concepts:
Concept | Definition | Commercial effect |
|---|---|---|
Gross size | Based on the smallest cuboid enclosing the block | Larger figure; crust, protrusions and irregular ends are included |
Net size | Based on the greatest regular cuboid that can be inscribed within the block | Smaller figure; close to the body that enters the saw |
Commercial size | The agreed invoicing basis derived from gross or net size after any agreed defect allowances or reductions | The figure actually invoiced; the contract must state whether it derives from gross or net dimensions |
Volume is then stated in m³. EN 1467 also provides that shapeless rough blocks are measured commercially by mass rather than by volume. The m³ logic in this section therefore applies mainly to approximately cuboid blocks.
The common shop-floor phrase "measure at the narrowest point" is a simplified description of net size; it does not replace the standard's definition. Practice varies from quarry to quarry and from contract to contract, so state the basis in writing rather than assuming it.
Sample clause for the offer or contract:
Invoicing shall be based on the commercial size within the meaning of EN 1467, derived from [gross / net] size. The final measurement shall be recorded in a loading report signed or otherwise approved by both parties and matched to the marked block numbers. Dimensions shall be recorded to 0.01 m, using the rounding method stated in the contract.
This is illustrative commercial wording and should be reviewed under the governing law of the contract.
Practical checks on the buyer's side:
Measurement should be recorded before or at loading and per block; a list showing only a single total m³ line is not sufficient.
The block number is painted on the block, matches the record, and is legible in the photographs.
How crust and irregular ends are treated in the commercial size must be stated separately.
Where mass-based measurement applies to shapeless blocks, the weighing method and its documentation should be defined in the contract.
2. Weight, loading and the container limit
Planning containers with slab logic is a common mistake in block buying. What constrains a block shipment is weight, not volume.
Indicative densities for preliminary planning:
Stone | Density (t/m³) |
|---|---|
Marble | 2.60 – 2.78 |
Travertine | 2.30 – 2.55 |
Limestone | 2.40 – 2.70 |
Onyx | 2.60 – 2.80 |
Basalt | 2.80 – 3.00 |
These ranges are for preliminary load planning only. Use the apparent density declared in the stone's EN 1936 test report for final calculations.
Example: a marble block of 2.80 × 1.60 × 1.50 m = 6.72 m³ → approximately 17.5 – 18.7 tonnes.
What follows from this:
Maximum payload on a 20 ft standard container is typically in the 27–28 tonne range, varying by carrier and container type (Hapag-Lloyd 20' Standard specifications). For marble that corresponds to roughly 9–10 m³. The exact figure must be confirmed from the payload marked on the container itself.
Consequently block shipments are usually made in 20 ft containers; a 40 ft container reaches its weight limit long before its volume is filled.
Floor load distribution, dunnage and lashing, and the road weight limits in the destination country must also be checked; moving the container from port to your plant is often more restrictive than the ocean limit.
Under SOLAS, a VGM (Verified Gross Mass) declaration is a prerequisite for loading the container onto a vessel. A gap between the declared and weighed figure creates delay and additional cost.
The weight of a single block must be compatible with the crane and forklift capacity at your facility.
3. Block sizes and machine compatibility
Whether a block suits your machine matters as much as its quality.
Marketable block size ranges commonly seen, for preliminary planning:
Length: 240 – 320 cm
Width: 130 – 190 cm
Height: 120 – 190 cm
These ranges are for preliminary planning; they are not a norm valid for every quarry or stone.
On the machine side:
Gang saw: the common method for bulk slab production. The block must fit the trolley and be as square and upright as possible. An out-of-square block is squared first, and that is a loss of volume.
Multi-wire: can provide a lower kerf and higher area yield than gang saws, depending on wire diameter, blade system, machine condition and stone type. This is not an advantage in every case — a system running 7.3 mm wire may leave a wider cut than some gang saw blades.
ST / circular-blade block cutter: suited to smaller, irregular blocks and cut-to-size production.
Stating which machine the block will be cut on improves the accuracy of the selection made at the quarry. Example: "For gang saw, 280 × 160 × 170 cm, minimum length 270 cm."
4. Quality: "first quality" is not binding on its own
There is no universal A/B/C block-grading standard applicable across Turkish quarries and suppliers; the labels in use are commercial terminology set by individual quarries and companies. The same "A grade" label can mean two different things at two different sources. We therefore recommend agreeing on criteria rather than grade names.
Four headings to define in the offer:
Colour reference: approved photo or sample number and the accepted tone range.
Geometry: minimum length/width/height and maximum accepted out-of-square.
Defect threshold: which defect is acceptable, and to what extent.
Remedy on non-conformity: block replacement, an agreed price or invoiced-volume adjustment, or rejection — which one applies.
With those four in writing, whatever grade label the other side uses becomes secondary.
5. Defect terminology and preliminary checks
When assessing blocks from photographs, it matters that both sides use these terms the same way.
Term | Meaning | Possible effect |
|---|---|---|
Hairline crack | Thin crack that may continue inward | Slab loss during cutting; risky because it is hard to detect from photos |
Open / structural crack | Visible separation | Usually the most serious defect; may lead to rejection or an agreed price or invoiced-volume adjustment |
Void / cavity | Internal hollow | Natural in travertine and managed by filling; problematic in marble |
Vein orientation inconsistent with the intended cutting direction | Vein running against the planned cut | Breaks pattern continuity; significant on large surfaces |
Iron / rust staining | Oxidising mineral | Colour staining over time; more critical on light-coloured stone |
Crust | Outer layer on the block surface | May fall inside gross size; treatment in commercial size depends on the contract |
Off-tone | Deviation from the approved shade | Inconsistency within the lot |
Two simple field checks:
Water test: the block is wetted; crack lines may become visible as it dries.
Hammer sound: the sound may become dull over a cracked area.
Both are surface-level preliminary checks only. They do not verify the internal structure of the block and do not substitute for an inspection report. Natural stone is a geological material, and the inside of a block cannot be fully known until it is cut. Defining that uncertainty in the contract is safer than arguing about it afterwards.
6. From invoiced m³ to saleable m²
You pay for a block in m³ and sell in m². Yield is the bridge. The most common mistake is deducting the same loss twice, so fix the denominator first.
Step 1 — Define the denominator
Yield should always be calculated against the invoiced commercial volume, because that is what you paid for.
If the commercial size derives from net size: do not apply a second generic gross-to-net or irregularity deduction. Include only actual pre-saw trimming, cutting allowance and other operational losses not already excluded from the invoiced dimensions.
If the commercial size derives from gross size: where possible, derive the gross-to-net adjustment from the measured net dimensions of the actual block rather than from a generic percentage.
Step 2 — Theoretical slab area
m²/m³ = 100 ÷ (sawn slab thickness in cm + actual cut width in cm)
Thickness caveat: use the thickness set at the saw, including any allowance required for calibration, polishing or finishing. Do not use the final finished thickness unless it is also the actual sawn thickness. If a 20 mm finished product is sawn at 21–22 mm, a calculation based on 20 mm systematically overstates yield.
Cut width varies by machine and by wire or blade. Multi-wire catalogues typically offer diamond wire diameters between 4.3 and 7.3 mm. Pedrini's Jupiter multiwire range lists wire diameters of 4.3, 5.3, 6.3 and 7.3 mm.
Important: nominal wire diameter is a planning reference, not a guaranteed kerf or a guaranteed plant yield. For purchasing calculations, use the plant's measured average cut width where available.
The table below is pure arithmetic:
Assumed sawn thickness | Assumed cut width | Theoretical area (m²/m³) |
|---|---|---|
2 cm | 4.3 mm | ~41.2 |
2 cm | 5.3 mm | ~39.5 |
2 cm | 6.3 mm | ~38.0 |
2 cm | 7.3 mm | ~36.6 |
3 cm | 4.3 mm | ~29.2 |
3 cm | 6.3 mm | ~27.5 |
These are calculation scenarios, not guaranteed machine kerfs.
Step 3 — Down to saleable area
What is deducted from the theoretical area depends on your plant and on the stone:
Slabs broken or separated along cracks during cutting
Slab edge trimming (net usable area)
Slabs rejected on colour or pattern
Additional waste driven by product size if you are going to cut-to-size
There is no single percentage that can be applied across the industry for these items. Use recent production records from blocks of the same quarry, selection, machine, sawn thickness and cutting orientation. The larger and more comparable the sample, the more reliable the expected yield. If you have no data yet, build the calculation as a scenario with an optimistic and a conservative case.
Step 4 — Compare both options at the same gate
The most common error when weighing block against ready slabs is comparing the delivered cost of the block against the FOB price of the slab. The two figures do not measure the same point. Build both as total lot cost ÷ saleable area:
BLOCK COST PER SALEABLE m²
Total non-recoverable landed and processing cost of the block lot
÷
Saleable slab area produced from that lot
SLAB COST PER USABLE m²
Total non-recoverable landed and handling cost of the slab lot
÷
Net usable slab area after trimming and rejection
Two points matter here:
Waste is not money; it reduces the denominator. Edge trim and rejected slabs are not added to the cost total — they shrink the saleable area.
Only non-recoverable duties and taxes are cost. Recoverable import VAT is usually not a true cost but a working-capital item, and should be assessed separately.
On top of that, the block option lengthens your cash cycle, ties up cutting capacity and leaves the waste risk with you. If the gap does not cover those three burdens, the commercial case for buying blocks weakens.
Buying blocks generally makes sense when:
You have your own cutting plant with spare capacity
You are targeting continuity and pattern integrity in a specific stone
You set product sizes according to your own market
Buying ready slabs generally makes sense when:
You have no cutting plant, or no guaranteed utilisation
You have a project-based, defined m² requirement
You do not want to carry the waste risk
7. What to send when requesting a block offer
Stone name or reference photo
Quantity (m³) and frequency (one-off / recurring)
Minimum and maximum block dimensions
Cutting method (gang saw / multi-wire / ST) and target sawn thickness
Accepted colour range and defect threshold
Whether commercial size derives from gross or net size
Target port and preferred Incoterms® 2020 rule
Required documents, where applicable: certificate of origin, A.TR or EUR.1, and inspection report
Target price level and delivery window
Note on Incoterms: EXW, FCA, FOB, CFR and CIF are used in block trade. "FOT" (free on truck) is not an Incoterms® 2020 rule. Where the seller loads the goods onto the buyer's collecting vehicle, FCA [named place], Incoterms® 2020 is generally the more appropriate recognised rule. The ICC recommends FCA over FOB for containerised cargo; where blocks move as break-bulk, FOB may remain suitable.
FAQ
Are blocks priced per m³ or per tonne?
Pricing practice varies by stone, quarry and supplier. The offer must state whether the commercial basis is m³ or tonnes, and where tonnage applies, the conversion density used.
How large is the difference between gross and net size?
It depends on how regular the block is, and no single ratio can be given. Because it feeds straight into price, the basis should be settled before the price is.
Is it safe to buy blocks from photographs?
Current, dated photos and video, a measurement record and matching block numbers reduce the risk substantially. But internal structure cannot be verified until the block is cut, so the defect threshold and the remedy for non-conformity must be defined in the contract.
How many blocks fit in a 20 ft container?
Weight decides, not volume. For marble, typically 9–10 m³ — one to three blocks depending on size. The exact figure is confirmed against the container's marked payload and carrier limits.
How many m² of slabs does 1 m³ of block produce?
At a 2 cm sawn thickness, theoretically ~36.6 – 41.2 m² depending on the assumed cut width. If an allowance is left for finishing (for example sawing at 21–22 mm for a 20 mm finished product), these figures fall. Operational yield may also be lower because of actual kerf, thickness tolerances, end cuts, machine settings and subsequent production losses. Saleable area should be calculated from your own cutting records.
Sources
EN 1467:2022 — Natural stone, Rough blocks, Requirements: BSI/ANSI preview · DIN EN 1467 record
Hapag-Lloyd — 20' Standard container specifications
IMO — Verification of the gross mass of a packed container (VGM)
Pedrini — Multiwire Jupiter GS240 · Multiwire Jupiter GS230
ICC Academy — Incoterms® 2020: FAS or FOB?
Density and block size ranges are for preliminary planning only; final calculations should rely on the stone-specific EN 1936 test report.
Next step
Send your block enquiry with the required dimensions, quantity, cutting method and destination port. We will check suitable Turkish sources and send current photos, measurements and a dated offer.
Verified Before Export — YaSeMarble