Hardwood is a term that often misleads beginning woodworkers. Many assume it means a wood that is physically harder, but the distinction is botanical, not mechanical. The USDA Forest Products Laboratory’s Wood Handbook explains that trees are divided into hardwoods and softwoods based on their reproductive and anatomical structures, not their density. Understanding this difference is the first step toward choosing the right material for furniture, flooring, or cabinetry.
What Makes a Wood a Hardwood?
According to the Wood Handbook, hardwoods are angiosperms, their seeds are enclosed in an ovary. Anatomically, they are porous, containing vessel elements that form continuous tubes for water transport. In temperate regions, hardwoods typically have broad leaves and are deciduous, though many tropical hardwoods are evergreen. Softwoods, by contrast, are gymnosperms with nonporous wood and usually needle-like leaves. The Wood Handbook notes that some softwoods, such as longleaf pine and Douglas-fir, are actually harder than hardwoods like basswood and aspen. So the label “hardwood” does not guarantee a harder material.
Hardwood resources in the United States are concentrated in the eastern states, with only a few commercial species found in Washington, Oregon, and California. The Wood Handbook lists major U.S. hardwood species by region, including red alder, ash, aspen, basswood, beech, birch, cherry, hickory, maple, oak, walnut, and yellow-poplar. Each species has distinct working properties, color, and grain, which influence its suitability for different projects. For a deeper look at wood selection, see our guide on choosing wood for woodworking.
Hardwood Lumber Grades and Dimensions
The Wood Handbook explains that hardwood lumber is primarily remanufactured into furniture, cabinets, flooring, and millwork. Grading rules, established by the National Hardwood Lumber Association (NHLA), are based on the proportion of a board that can yield clear cuttings. The highest grade is FAS (Firsts and Seconds), which requires at least 83-1/3% of the surface to be clear face material. Next is F1F (FAS one face), then Selects, followed by No. 1 Common, No. 2A Common, and lower grades. For No. 1 Common, the minimum clear-face yield is 66-2/3% for wider boards. The grading system is detailed in the NHLA rules, which are written in inch-pound units.
Standard lengths for hardwood lumber are in 1-foot increments from 4 to 16 feet (1.2 to 4.9 m). Widths are generally random, but each grade has a minimum width: FAS and F1F require at least 6 inches (152 mm), Selects 4 inches (102 mm), and No. 1 Common and lower 3 inches (76 mm). The Wood Handbook also provides standard thicknesses for rough and surfaced lumber. When buying hardwood, understanding these grades helps you balance cost and yield. For more on lumber types, visit our hardwood materials page and the broader wood and materials section.
Moisture, Shrinkage and Movement
Wood’s relationship with moisture is critical for woodworking. The Wood Handbook defines moisture content (MC) as the mass of water in wood divided by the mass of oven-dry wood, expressed as a percentage. Green wood can have MC ranging from about 30% to over 200%, depending on species. For example, green heartwood of American beech averages 55% MC, while its sapwood averages 72%. The fiber saturation point (FSP) is the moisture content at which cell walls are fully saturated but no free water remains in cell cavities. The Wood Handbook states that from a practical standpoint, most wood properties begin to change below about 30% MC, though the exact FSP varies by species and measurement method.
As wood loses moisture below the FSP, it shrinks. The Wood Handbook provides equilibrium moisture content (EMC) tables showing how wood’s MC changes with relative humidity and temperature. For instance, at 70°F (21°C) and 50% relative humidity, wood reaches an EMC of about 9%. Woodworkers must allow lumber to acclimate to the shop environment before use to minimize movement after assembly. The Wood Handbook notes that protective coatings can retard moisture changes but not prevent them entirely. For guidance on managing moisture and selecting stable wood, see our article on choosing wood.
Finishing Hardwoods
Hardwoods vary in grain structure, which affects how they accept stains and finishes; our finishing guides explain how pore size and fillers come into it. Always follow manufacturer instructions for any finish, and be aware that oil-soaked rags can self-heat and ignite. Northamptonshire Fire and Rescue warns that rags soaked in linseed oil or other drying oils can spontaneously combust if not disposed of properly. The fire service advises hanging them outdoors to dry, soaking them in water and sealing them in a plastic bag, or keeping them in an airtight metal container. For more on finishing, explore our wood finishes guide.
Health and Safety: Wood Dust
Hardwood dust poses health risks. OSHA’s Woodworking eTool reports that exposure to wood dust can cause dermatitis, allergic respiratory effects, asthma, and even nasal cancer. Certain hardwoods, including oak, mahogany, beech, walnut, birch, elm, and ash, have been associated with nasal cancer in woodworkers, particularly with high exposures. OSHA’s permissible exposure limit for nuisance dust is 15 mg/m³ total dust over an 8-hour time-weighted average, while NIOSH recommends a stricter 1 mg/m³. The eTool emphasizes that local exhaust ventilation (LEV) is the primary control method, capturing dust at the source. Sanders, shapers, and routers generate the most dust, and conventional exhaust methods are often inadequate. NIOSH has developed innovative controls, but they are not yet widely available.
For a home shop, applying OSHA’s guidance means using a dust collector with adequate airflow, keeping duct velocity between 2,500 and 4,000 feet per minute to prevent clogging, and regularly inspecting ducts and filters. Always wear a properly fitted respirator when sanding or machining hardwoods, and use eye and hearing protection. Keep the shop clean to reduce airborne dust accumulation. Our dust collection page and safety equipment guide offer practical advice for setting up a safer workspace.
Frequently asked questions
Is hardwood always harder than softwood?
No. The Wood Handbook explains that hardness is not the defining characteristic. Some softwoods, like longleaf pine, are harder than hardwoods such as basswood. The terms refer to botanical differences: hardwoods are angiosperms with porous wood, while softwoods are gymnosperms with nonporous wood.
What hardwood grade should I choose for furniture?
FAS and Selects grades yield the most clear material, making them suitable for visible furniture parts. No. 1 Common can be economical if you can work around knots and defects. The choice depends on your project’s size and the amount of waste you can accept.
How do I prevent hardwood from warping after I bring it home?
Allow the wood to acclimate to your shop’s humidity for several days or weeks, stacked with stickers for air circulation. The Wood Handbook’s equilibrium moisture content data shows that wood will eventually reach a moisture content in balance with the surrounding air. Keeping your shop at a stable relative humidity minimizes movement.
For more on hardwood species, grades, and safe handling, visit our hardwood category page.
