Ask five suppliers what size a “typical” timber mat is, and you’ll likely get five slightly different answers. That’s part of the problem. Thickness and sizing aren’t just what a vendor tells you; they determine how much load a mat can carry, how long it survives on your site, and whether what you’re buying is actually capable of supporting the equipment you plan to put on it. Get this wrong, and you’re not just buying a mat that wears out faster; you’re putting equipment on a support that was never rated to hold the real loads it sees at the ground.
This is one of the more technical pieces in our mat series, so we’re going to walk through how thickness and dimension work, how they interact with species and grade, and what to actually check before a truckload of mats shows up on your site.
What Actually Makes Something a “Timber” Mat
Before getting into thickness, it’s worth being precise about a term suppliers use loosely: timber mats. A true timber is defined as 5 inches by 5 inches or larger; anything under that is lumber, not timber. That distinction matters, because a mat built from a mix of true timbers and undersized lumber pieces isn’t a timber mat, regardless of what it’s marketed as or how it’s priced.
If you’re paying timber mat pricing, you should be getting actual timber dimensions throughout the mat, not a mix that quietly cuts capacity and service life while still being sold as “typical”.
Typical Thickness Options and What They’re Really Rated For
Engineers don’t work with “weight capacity” or thickness as a single number stamped on the side. They work with bending strength (modulus of rupture, MOR, in PSI), thickness, species characteristics as measured by recognized third parties like the American Wood Council or the US Forest Service Laboratory, and how the load spreads across the mat and into the ground. In simple terms, capacity changes with the square of the thickness times the material strength, which is why an inch of real thickness matters more than the nominal size suggests.
#4‑inch mats
4‑inch mats are the lightest option and belong in light duty: foot traffic, light equipment access, and temporary surfaces where heavy machinery isn’t crossing directly. They’re easier to handle and cheaper per mat, but in most species they’re not rated for the concentrated outrigger or track loads that cranes, rigs, or heavy construction equipment put down, and using them under that kind of equipment is a compliance and safety problem, not just a wear issue. Typical options are three-ply laminated mats and cross-laminated (CLT) mats.
#6‑inch mats
6‑inch mats sit in the middle and cover a wide range of general construction and access road use. For utility trucks, small excavators, and typical vehicle traffic, a properly rated 6‑inch mat in many species usually has margin to spare, which is why this thickness often makes sense where you need real load capacity without the weight and freight cost of the heaviest option. There are a few manufacturers who make a solid, 6-inch three-ply laminated mat, sometimes even of oak. World Forest Group makes a solid timber 6” mat too.
#8‑inch (and thicker) mats
8‑inch mats are typical for heavier work: right‑of‑way projects, heavier equipment, and applications where concentrated point loads from outriggers or track edges are the real design driver. This is where species and grade matter as much as the thickness number itself, because a #2 hardwood around 550 PSI behaves very differently than a higher‑PSI species like Eucalyptus at roughly 2,000 PSI under the same load.
For cranes, rigs, and anything putting significant load through outriggers, neither 6‑inch mats nor typical 8‑inch, low‑PSI mats are sized for the job. That’s why 10‑ to 12‑inch high‑PSI mats are typical in that equipment class: not because thicker is automatically better, but because species, grade, and thickness together are what handle the point loads and satisfy OSHA’s ground conditions requirement.
The part buyers usually miss: thickness alone doesn’t tell you the load rating. Two 8‑inch mats from two different suppliers can have very different capacities depending on species and grade, which is why you should always ask for the documented MOR/PSI rating, not just the thickness number.
Typical Width and Length – And Why “True” Dimensions Matter
Width is nominally 48 inches, with length typically at 16 feet or 18 feet or 20‑foot mats used in specific applications that need a longer span. The word “nominal” is doing a lot of work there; undersized dimensions are more common in this industry than most buyers expect, and they’re not harmless rounding errors.
Capacity depends on depth and how the load spreads across the full surface area. If a mat is sold as 8 inches thick but actually measures 7 inches, you’ve lost roughly 25% of its load‑bearing capacity because the thickness term is squared in the capacity calculation (8×8 = 64; 7×7 = 49).
Here’s the part worth double‑checking every time: confirm your supplier is shipping true 48‑inch by the specified thickness by 16‑ or 18‑foot mats, not slightly undersized versions marketed as “standard”. If you want the full breakdown on why true 48‑inch mats matter, we’ve laid it out in detail in our sizing guide on savings from true‑size mats.
How Species and Grade Drive Sizing Decisions
Thickness and species aren’t independent decisions; they work together. A mat’s actual capacity is bending strength, thickness, and how loads spread across the surface and into the ground.
Oak at #2 grade runs around 550 PSI bending strength; at #1 grade it’s closer to 1,000 PSI, using American Wood Council National Design Specification values.
Eucalyptus is a different animal: tighter grain, higher density, and MOR ratings closer to 2,000 PSI, roughly double a #1 oak mat at the same thickness.
That’s why an 8‑inch oak mat and an 8‑inch Eucalyptus mat are not interchangeable, even though the thickness spec looks identical. At 10 or 12 inches, that gap gets even more pronounced; it’s often possible to substitute a 10‑inch Eucalyptus mat for a 12‑inch mixed hardwood mat, and in some cases one 12‑inch Eucalyptus mat can replace two 12‑inch mixed hardwood mats under the same load.
If your equipment loads are heavy and your project runs long, matching species and grade to thickness usually delivers more value than simply “going thicker.” A poorly matched species at 8 inches can still underperform a well‑matched, higher‑PSI species at a more moderate thickness under the same conditions.
Matching Thickness to Your Equipment (and Ground)
The right way to size mats is to work backward from your actual loads, not from thickness alone or total equipment weight on a spec sheet. OSHA 1926.1402 treats ground conditions like slope, compaction, and firmness, and supporting materials like mats as part of the same requirement, which means this is a compliance question as much as a practical one.
- -Cranes and rigs: Outrigger pads and rig supports concentrate enormous point loads into small contact areas, often far exceeding what the equipment’s total weight would suggest if you spread it evenly across the ground. This is why 12‑inch, high‑PSI mats are the typical for large cranes and similar rigs; under-sizing this application isn’t a minor risk; it’s exactly how mats fail in the field.
- General construction and access roads: For utility trucks, small excavators, and typical vehicle traffic, a properly rated 6‑inch mat in many species usually has margin to spare, and is often the more cost‑effective choice.
- Foot traffic and light equipment: 4‑inch mats are sufficient here. Specifying 8‑inch, high‑PSI mats for walkways and light-duty zones isn’t wrong; it’s just paying for capacity you’ll probably never use.
Ground conditions change what a mat can actually do. A PSI rating assumes reasonably stable, well‑prepared ground underneath. Soft, saturated, or uneven ground reduces what a mat can deliver, which is why wetland or seasonal‑flood sites usually need more safety margin than the equipment weight alone would suggest. Skip that step, and you can end up with a correctly rated mat still sinking or shifting under load.
Sizing and Total Cost of Ownership
Thickness doesn’t just affect performance; it drives cost at every step. Thicker mats weigh more, and weight is a direct freight cost. At roughly $1,500 per truckload, fitting fewer mats per load because they’re oversized for the application adds up quickly across a multi‑mile project, especially when you over‑spec thickness in zones that don’t need it.
Get capacity wrong on the low side, and you risk mat failure, downtime, and safety incidents—all of which cost more than the mat ever would. Get it wrong on the high side, and you’re paying for weight you don’t need and losing mat count per truck. Matching thickness and species to real load requirements avoids both problems.
If you want to model this against your own project scale, our total cost of ownership calculator factors in weight, freight, and mat life together instead of looking at thickness or unit price in isolation, and our freight savings tool lets you see the impact of thickness and size on trucking alone.
| Thickness | Typical use | Load level | Weight note |
| 4 inches | Foot traffic, light equipment access, temporary walkways | Light | Lightest, easiest to handle by hand |
| 6 inches | General construction, typical access roads, vehicle traffic | Moderate | Balanced weight-to-capacity ratio, good for mixed sites |
| 8–12 inches | Crane pads, rig mats, heavy equipment, outrigger and track support | Heavy | Heaviest; freight cost and mat count per load shift accordingly |
Treat this as a starting point, not a substitute for matching thickness to your actual equipment specs, ground conditions, and species/grade selection. A supplier who can’t tell you the MOR/PSI rating behind a given thickness and species combination isn’t giving you enough information to make the sizing call properly.
Sizing by Industry
Different sectors hit mats with different patterns of load, duration, and ground conditions. The logic doesn’t change; bending strength plus ground bearing capacity, but how you apply it does.
Oil and gas: Rig mats almost always call for 8‑inch thickness given drilling equipment loads, and multi‑year use with repeated moisture cycling. Here, pairing thickness with a higher‑rated, rot‑resistant species matters as much as thickness itself.
Utility and pipeline work: Sizing usually varies by segment of the route. Wetland crossings may call for wider or higher‑PSI mats to distribute load over softer ground, while upland sections crossed by lighter equipment may only need 6‑inch mats with moderate PSI ratings. From a practical viewpoint, mixing 6” and 8” mats may not be feasible on short ROWs. On long ones, where you use lots of mats, it may make sense.
- Construction: Sizing should follow the heaviest concentrated load expected on site, not the average. A site that occasionally uses a large crane still needs higher‑capacity mats in that zone, even if most daily traffic is lighter trucks and excavators.
- Renewable energy (solar): Large sites where mats are repositioned repeatedly often benefit from thinner mats like 4-inch or 6‑inch mats where loads allow, since the weight savings across hundreds of moves add up in labor, equipment wear, and freight. Wind is different, as most wind lifts are big cranes lifting large loads. They’ll need 8” mats minimum, often stacked or 12” mats.
Common Mistakes in Mat Sizing
A few patterns show up again and again:
- Assuming “typical” always means OK. Check the actual specifications!
- Comparing thickness without comparing species or grade. Two mats at the same thickness can have very different MOR ratings depending on species and grade, which makes them different products once you put equipment on them.
- Not verifying true dimensions on delivery. Spot‑check incoming mats against the quoted spec; a “48‑inch” mat that measures 46 inches or an “8‑inch” mat that measures 7 inches isn’t a rounding error; it’s a real reduction in rated capacity.
- Using one thickness across an entire project regardless of zone. Very large projects with mixed‑use sites, a staging area next to a crane pad, for example, might benefit from mixing thicknesses by zone instead of defaulting to one spec everywhere, which avoids paying for 8‑inch or 12” capacity in areas that only ever see foot traffic.
- Skipping documented MOR/PSI ratings from suppliers. Thickness is not a substitute for verified engineering values specific to species and grade.
Making the Call
Thickness is only one piece of the sizing equation. What actually determines whether a mat performs is thickness, species, grade, true dimensions, and ground conditions working together, matched to your specific equipment loads. The exercise worth doing before you order is simple: identify your heaviest concentrated load—outriggers, track edges, tire patches—size for that number with a safety margin, and use lighter mats where the load doesn’t demand more.
Even better: Ask your engineer to do the work. S/he knows!
For a full breakdown of how mat types compare across species, thickness, and capacity, see our timber mat types comparison guide, or run your own numbers through the total cost of ownership and freight savings calculators before your next order.