Hardness: what Janka actually tells you
The Janka rating measures the force needed to embed a steel ball halfway into the wood. Oak sits around 1360 and pine around 540 — roughly two and a half times softer.
Soft wood dents and bruises; hard wood resists wear but blunts edges faster and is harder to work. Match the species to the abuse the piece will take, not to a prestige ranking.
Stability: the number nobody checks
Shrinkage figures matter more than hardness for wide panels and doors. Beech moves nearly 30% across its width between green and dry; MDF moves around 6%.
For anything large and flat that must stay flat, favour a stable species or a manufactured board. For narrow parts, movement matters much less.
Workability and what it costs you
Some species are simply pleasant: cherry, poplar and tulipwood machine cleanly and take a finish evenly. Others fight back — sapele tears out on figured sections, teak dulls edges and resists glue, MDF fills the shop with fine dust.
Cheap species that are easy to work are ideal for learning. Expensive species reward skill but punish impatience.
Outdoor use is not about hardness
Rot resistance comes from natural oils and extractives, not from density. Teak, iroko, western red cedar and white oak all perform outdoors; hard maple, beech and ash do not, however hard they are.
Even rot-resistant species benefit from raised end grain and a finish that is maintained rather than perfect.
