How to read a Janka hardness number
By Lucas Anderson · Published · Data: Wood Handbook 2010
A Janka hardness number is the force needed to press a steel ball halfway into a piece of wood. The higher it is, the better the wood resists dents. In the Wood Handbook the figures run from 240 lbf to 3,680 lbf, with a median of 950 lbf, so anything above about 1,000 lbf is already harder than most woods listed.
What the test measures
The Janka figure on every TimberLedger page is side hardness. A steel ball 0.444 inch across is pressed into the face of a small, clear, dry specimen until half of the ball is buried, and the force it took is recorded. The bigger the force, the better the wood resists a dent from a dropped tool, a chair leg or a heel. The Wood Handbook reports that force in pounds-force (lbf); the metric version is in newtons, and the conversion is a fixed 4.448 N per lbf. That is why white oak reads 1,360 lbf on one chart and 6,050 N on another: same test, different unit.
The moisture content matters. The values we rank are for wood at 12% moisture content, roughly the state of seasoned lumber indoors. The handbook also lists hardness for green, freshly cut wood, and for 147 of the 155 woods we have both figures. In those 147, the dry value is higher by a median of 31%. The spread is wide: Indian rosewood gains 103% on drying, while primavera, macawood and afrormosia test slightly lower dry than green. A green figure set against a dry one can therefore be off by about a third. Every number on this site is the 12% value.
Where a number sits on the scale
A Janka figure is easier to judge once you know the spread. Across the 155 woods the lowest is ceiba at 240 lbf and the highest is ipe at 3,680 lbf, about 15 times as hard. Most woods sit well below the middle of that range. The median is 950 lbf: half of the woods are softer, half harder. A quarter of them measure under 565 lbf, and only a quarter exceed 1,465 lbf.
The shape explains a lot of everyday confusion. Of the 155 woods, 80 come in under 1,000 lbf, so a wood in the low thousands is already harder than most of the list. Above 2,000 lbf there are just 18 woods, and the seven at 3,000 or more are all imports. On the full Janka scale you can see the same pattern as dots: a dense crowd on the left and a thin tail to the right.
Red oak as the yardstick
A number on its own says little, so flooring and furniture writers usually compare it with northern red oak, which the handbook puts at 1,290 lbf. TimberLedger does the same: every species page states the wood as a percentage of red oak. Of the other 154 woods, 102 are softer than red oak and 50 are harder; the rest tie with it. So red oak sits in the harder third of the list, not in the middle, which is worth remembering when a wood is described as “softer than oak.”
| Wood | lbf | Newtons | vs red oak | Rank |
|---|---|---|---|---|
| Eastern white pine | 380 | 1,690 | 29% | 144th |
| Yellow-poplar | 540 | 2,402 | 42% | 119th |
| Black cherry | 950 | 4,226 | 74% | 77th |
| Black walnut | 1,010 | 4,493 | 78% | 74th |
| Teak | 1,000 | 4,448 | 78% | 75th |
| Northern red oak | 1,290 | 5,738 | 100% | 51st |
| White oak | 1,360 | 6,050 | 105% | 45th |
| Sugar maple | 1,450 | 6,450 | 112% | 41st |
| Shagbark hickory | 1,880 | 8,363 | 146% | 22nd |
| Jarrah | 1,910 | 8,496 | 148% | 21st |
| Ipe | 3,680 | 16,369 | 285% | 1st |
Reading the gap between two numbers
When two woods are compared, the percentage tells you more than the raw difference. White oak at 1,360 lbf is 5% harder than red oak, a small gap. Sugar maple at 1,450 lbf against black cherry at 950 lbf is a 53% gap, and that one is large. The same 100 lbf means different things at each end of the scale: going from 380 lbf to 480 lbf is a 26% step, while 3,580 lbf to 3,680 lbf is under 3%.
Ties are common, because the handbook gives every hardness figure in steps of 10 lbf. Black cherry and red maple both list 950 lbf, and five woods share 350 lbf near the soft end. Two woods a few dozen pounds-force apart are, for practical comparison, about equally hard; the ranks on this site count ties together so that neither is pushed ahead.
What the number does not tell you
The Janka figure is an average from small, clear, straight-grained pieces. It says nothing about knots, grade or the finish on top, and it is not a structural value. It also measures one thing only: resistance to an indent. A wood can be hard yet shrink a lot as it dries (shagbark hickory, 1,880 lbf, loses 10.5% across the face), or soft yet stay steady (redwood (old-growth), 480 lbf, 4.4%). For figures on the imported woods, the handbook notes that they were taken from world literature rather than tested at the Forest Products Laboratory, so small differences between imports deserve less weight than the same gap between two U.S. species.
To see a wood’s hardness next to its density, strength and movement in one view, put it in the comparer, or use the finder to list every wood inside a Janka range you choose. For why heavier woods tend to be harder, see Density and hardness: how closely they track.
Sources and method
USDA Forest Service, Forest Products Laboratory. Wood Handbook: Wood as an Engineering Material (2010, FPL-GTR-190), Tables 4-3 and 4-4 (shrinkage) and 5-3b and 5-5b (strength and hardness). Public domain. Medians, counts, ranks, correlations and percentages are calculated by TimberLedger from those tables across the 155 woods on this site. Data as of: Wood Handbook 2010 edition (published test averages of small clear specimens). How we use the data.