Why hardwood grading matters for buyers
A cubic metre of oak can be worth very different amounts depending on what it contains. Knots, sapwood, splits, wane and colour decide whether a board becomes a visible tabletop, a hidden frame member or firewood. Grading rules turn those features into a shared language, so that buyer and seller mean the same thing when they say "first grade".
The problem is that there are several languages. A furniture maker in Germany may be used to EN 975-1 classes, an importer of American timber to NHLA grades, and a Romanian sawmill to "clasa A" or "calitatea I". This guide explains the two formal systems, the main features they measure and how to write a specification that buys the grade you need, not the grade you were sold.
Two systems: NHLA in North America, EN 975-1 in Europe
The two systems start from different questions.
- NHLA (National Hardwood Lumber Association) rules ask: how much of this board can I cut into clear pieces? The grade depends on the share of the board's surface that yields clear-face cuttings of a minimum size. NHLA was founded in 1898 and switched to this cutting-unit basis in 1932.1
- EN 975-1 asks: which features does this piece have, how big and how many? It sets limits on knots, sapwood, splits, wane and other features for each grade. It was published in 2009 with a 2010 corrigendum, and appears in Germany as DIN EN 975-1:2011-08. Part 1 covers oak and beech.2
Because one system counts usable area and the other counts features, there is no official conversion table between them. An FAS board and a Q-F1b strip are both high grades, but they describe different things.
NHLA grades explained: FAS, Selects, No. 1 Common, No. 2A Common
NHLA grades apply to "Factory lumber", meaning boards bought to be cut into smaller parts. In descending order the grades are FAS (Firsts and Seconds), F1F (FAS One Face), Selects, No. 1 Common, No. 2A and 2B Common, No. 3A and 3B Common, and Sound Wormy.1 Except for F1F and Selects, the inspector grades the poorer face of the board.1
The cutting-unit idea
The grader imagines the board cut into clear rectangles ("cuttings"), each at least a minimum size. FAS requires that at least 83⅓% of the board's surface can be cut into clear-face cuttings at least 4 in × 5 ft (about 102 mm × 1.52 m) or 3 in × 7 ft (76 mm × 2.13 m). No. 1 Common requires 66⅔% in cuttings of at least 4 in × 2 ft or 3 in × 3 ft. No. 2A Common requires 50%, in cuttings of at least 3 in × 2 ft.1 The more and larger the clear pieces a board will yield, the higher the grade.
The grade also sets the minimum board size. FAS and F1F boards must be at least 6 in (152 mm) wide and 8–16 ft (2.4–4.9 m) long. Selects start at 4 in (102 mm), and the Common grades at 3 in (76 mm) and 4 ft (1.2 m).1
| Grade | Lengths | Minimum width | Clear-face yield | Minimum cutting size |
|---|---|---|---|---|
| FAS (and F1F) | 2.4–4.9 m (8–16 ft) | 152 mm (6 in) | 83⅓% | 102 mm × 1.52 m or 76 mm × 2.13 m |
| Selects | 1.8–4.9 m (6–16 ft) | 102 mm (4 in) | As F1F on the good face; reverse face not below No. 1 Common | As FAS |
| No. 1 Common | 1.2–4.9 m (4–16 ft) | 76 mm (3 in) | 66⅔% | 102 mm × 0.61 m or 76 mm × 0.91 m |
| No. 2A Common | 1.2–4.9 m | 76 mm | 50% | 76 mm × 0.61 m |
| No. 3A Common | 1.2–4.9 m | 76 mm | 33⅓% | 76 mm × 0.61 m |
| No. 3B Common | 1.2–4.9 m | 76 mm | 25% (sound cuttings) | 38 mm wide, at least 232 cm² |
Summary only. The full NHLA rule book has exceptions and species-specific rules. Source: Forest Products Laboratory (2021), Wood Handbook, FPL-GTR-282, chapter 6, table 6-1 and minimum widths. Metric values converted by SARAL from the inch-pound rules.
Inches, quarters and random widths
NHLA rules are written only in inch-pound units. Standard lengths run in 1-ft (305 mm) steps from 4 to 16 ft, and boards are sold in random widths.1 Thickness is given in quarters of an inch. A "4/4" board is 25 mm rough and about 21 mm when surfaced on both sides, and "8/4" is 51 mm rough and 44 mm surfaced.1 When you compare American and European offers, compare the finished thickness you will get, not the nominal one.
Cut-to-size parts follow other rules. American hardwood dimension parts are graded under the rules of the Wood Components Manufacturers Association, with grades such as Clear two faces, Clear one face, Paint and Core.1
EN 975-1: appearance grading of oak and beech
EN 975-1 covers sawn oak and beech. Its structure is the same for both species. It sets out the criteria to be assessed: wood structure, sawing characteristics, warp, fungal and insect attack, stains and other features. It then names the grades for oak (Q) and beech (F), sets rules for accepting batches of unedged and square-edged timber, and ends with the grading tables.2 The standard itself is sold by the standards bodies. The oak values below come from a leaflet published by the French oak promotion association APECF and French Timber, which summarises the standard.3
Reading an oak grade code
An oak grade such as Q-F 2 X has up to four parts.3
- Q for Quercus, oak.
- The product type: B for boules (logs sawn through and kept together, unedged), S for selected unedged boards, F for strips and square-edged timber up to 41 mm thick, and P for beams with thickness plus width of at least 200 mm and a thickness of at least 80 mm.
- The grade: A for exceptional quality, then 1 to 4 in decreasing order. Strips have 1a and 1b at the top.
- X or XX at the end: sound sapwood on one face or on both.
Knot limits for oak strips and square-edged timber
Strips (40–99 mm wide) and square-edged boards (100 mm and wider) are graded on their best face. For pieces narrower than 120 mm the leaflet gives these limits, with one extra knot allowed for every further 40 mm of width.3
- Q-F 1a: straight grain, one sound knot under 10 mm. Up to 20% of pieces may have one extra sound knot.
- Q-F 1b: practically free of features other than sound knots; three knots under 12 mm. Sound knots under 5 mm are ignored.
- Q-F 2: three knots under 25 mm.
- Q-F 3: three knots under 40 mm, plus one dead or unsound knot under 20 mm and wane under 3 mm. Bark pockets, brown pith, rot and holes are excluded.
- Q-F 4: sound knots under 70 mm without limit, two dead or unsound knots (under 35 mm and under 20 mm), and wane up to 10% of the width and 20% of the length. Rot and holes are excluded.
From Q-F 1b down, EN 975-1 also uses an equivalence rule. Any distribution of knots is accepted as long as each knot is below the maximum size and their diameters together stay below the permitted total. In Q-F 2, for example, three knots of 25 mm add up to 75 mm. Four 10 mm knots, one 15 mm and one 20 mm knot therefore pass too.3 Knot size for appearance grading is the average of a knot's largest and smallest diameter.3
Unedged oak: the 0.20 × 2.0 m rectangle
Unedged boards and boules are graded differently. The grader places a virtual rectangle of 0.20 m × 2.0 m on the grading face where it contains the most, or the worst, features. Features less than 10 cm from the edges or ends are generally ignored.3 A boule is accepted at its stated grade if at least 65% of it meets that grade, under 25% is one grade lower and under 10% two grades lower.3
| Grade | Knots permitted | Minimum boule width |
|---|---|---|
| Q-B A / Q-S A | One sound knot under 20 mm | 350 mm |
| Q-B 1 / Q-S 1 | Under 5 mm if fewer than eight; 5–25 mm if together equivalent to one knot under 50 mm | 250 mm |
| Q-B 2 / Q-S 2 | Under 5 mm without limit; 5–40 mm if equivalent to one knot under 100 mm | 250 mm |
| Q-B 3 / Q-S 3 | Under 10 mm without limit; 10–70 mm if equivalent to one knot under 160 mm | 250 mm |
| Q-B 4 / Q-S 4 | No restriction unless the contract excludes features | 250 mm |
Minimum length 2 m for all boule grades. Other features (shakes, bark pockets, brown pith, rot) are limited separately. Source: French Timber and APECF (2012), Grading of Sawn Timber: Oak, appearance grading to EN 975-1 (2009). Leaflet summary of the standard; sound knots only.
Boules also have size rules. The central board must be at least 350 mm wide for Q-B A and 250 mm for Q-B 1 to Q-B 4, and the minimum length is 2 m.3
Oak beams and strength classes
Beams are graded Q-P A, Q-P 1 and Q-P 2. These are still appearance grades, not strength grades. French grading campaigns on oak beams thicker than 100 mm matched them to the EN 338 strength classes D30, D24 and D18. In France, structural oak is graded visually under NF B 52-001 or by machine, and structural sawn timber must carry CE marking.3 If a beam carries load, specify a strength class, not an appearance grade.
Beech grades
EN 975-1 gives beech its own grade names, beginning with F for Fagus, and its own tables.2 We could not check the beech limits against an open source, so we do not print them here. Ask your supplier to state the beech grade and send the relevant table. For beech, colour usually matters as much as knots: red heart and the difference between steamed and unsteamed timber are covered in our beech wood guide.
Grading logs: EN 1316-1 and log quality classes
Sawn-timber grades start with the log. EN 1316-1:2012 classifies felled round timber of sessile oak, pedunculate oak and beech by quality where the end use is not yet known. Companion parts cover poplar (EN 1316-2) and ash and maples (EN 1316-3).5 German state forests sell logs in quality classes A, B and C, and the official German log price index is published for these classes.6
The price spread between log classes is large. In the state forests of Baden-Württemberg in 1999, A-grade made up less than 5% of beech sawlogs and C-grade 58%. Average prices were €351 per m³ for A, €111 for B and €45 for C. The main reason for downgrading beech was red heart, a discoloured core that develops in older and thicker trees. Below about 60 cm diameter and 120 years of age, devaluation through red heart was rarely a concern.4 The prices are a quarter of a century old, but the ratio shows how strongly grade drives value.
Features that decide a grade
Whatever the rule book, the same features decide most grades in oak and beech.3
- Knots. Sound, intergrown knots are tolerated more than dead, loose or unsound knots. Size, number and spacing all count.
- Sapwood. In oak, the pale sapwood is less durable than the heartwood. Sound sapwood is allowed in many grades but marked with X or XX in EN 975-1.
- Splits and shakes. End splits, ring shake (separation along a growth ring) and frost cracks limit higher grades.
- Pith and heart. Brown pith and boxed heart (a piece containing the pith) are excluded from the upper grades.
- Wane. Bark or missing wood on an edge. It is allowed only in small amounts in the lower square-edged grades.
- Rot, holes and bark pockets. Usually excluded or tightly limited.
- Colour. In beech, red heart and uneven colour; in oak, colour differences between boards. These matter for visible surfaces and should be specified separately.
Trade terms: Prime, Select, Natural, Rustic, AB/B/C
Flooring, panel and worktop makers often sell by names such as "Prime", "Select", "Natur", "Rustic" or "AB", "B", "C". German buyers search for "Eiche AB-Qualität" or "Eiche C-Qualität", and Romanian buyers for "cherestea clasa A". None of these names belongs to EN 975-1 or NHLA. Each company, and sometimes each product line, defines them in its own way. "Rustic" in one catalogue may allow knots that another calls "Natural".
Such names are useful shorthand once both sides have seen the definition. Before that point, they are a marketing label. Ask for the written definition, with knot sizes, sapwood, filled defects and colour range, and for photographs of real boards.
Grade, yield and price: choosing the right grade
A higher grade costs more per cubic metre but yields more usable wood per cubic metre. The right choice depends on the cutting bill, meaning the list of part sizes you will cut.
- Long, wide, visible parts such as tabletops, stair treads or continuous-lamella panels need the long clear cuttings that only the top grades guarantee.
- Short parts such as chair rails, drawer sides and finger-jointed lamellas can come from lower grades, because the clear pieces between knots are long enough. NHLA's No. 1 Common only promises cuttings of 2–3 ft (0.61–0.91 m), which is plenty for many furniture parts.1
- Hidden parts such as frames, cores and battens can accept sound knots and colour variation.
Buying the top grade for every part means paying for clear wood that ends up as offcuts. Buying too low a grade means paying for wood that becomes waste. The economic answer is usually a mix of grades, cut on an optimising saw that removes defects and maximises the yield of each board. Our article on yield and optimisation from log to part covers how much a board yields at each stage.
How we sort and optimise at SARAL
How to write a purchase specification
- Name the rule and the edition. For example "EN 975-1:2009, grade Q-F 1b" or "NHLA rules, FAS". Do not write "first quality" alone.
- Name the species precisely. European oak (Quercus robur or Q. petraea) is not American white oak, and European beech (Fagus sylvatica) is not American beech.
- State the product form. Unedged, square-edged, strips or beams, with thickness and width ranges, length range and whether widths are random or fixed.
- State sapwood and colour separately. For oak, say whether sapwood (X or XX) is accepted. For beech, say whether red heart is accepted and whether you need steamed or unsteamed timber.
- Specify moisture. Grading says nothing about moisture. Ask for a target moisture content and tolerance; see our article on kiln drying hardwood.
- Agree acceptance. How many pieces may fall below grade, who inspects and what happens if a batch fails.
- For trade grades, attach the definition. If you buy "AB" or "Rustic", attach the supplier's written definition and reference photos to the order.
Frequently asked questions
What does FAS mean in lumber?
FAS stands for "Firsts and Seconds", the highest NHLA grade for hardwood lumber. An FAS board is at least 6 in (152 mm) wide and 8–16 ft (2.4–4.9 m) long, and at least 83⅓% of its surface can be cut into large clear-face pieces.1
Is FAS the same as EN 975-1 grade Q-F 1a?
No. NHLA measures the share of clear cuttings a board yields; EN 975-1 limits the size and number of features. Both are top grades, but there is no official conversion between them. Specify one rule and grade.
What is the difference between No. 1 Common and No. 2A Common?
No. 1 Common must yield at least 66⅔% of its surface in clear cuttings of at least 4 in × 2 ft or 3 in × 3 ft. No. 2A Common must yield 50%, in cuttings of at least 3 in × 2 ft.1
What do "clasa A" or "Eiche AB" mean?
They are trade terms, not standard grades. Their meaning depends on the supplier. Ask for the written definition, or specify an EN 975-1 or NHLA grade instead.
