A timber beam has two jobs, and they are measured by two different numbers. Stiffness decides how far it sags under the load it already carries; strength decides the load at which it breaks. The database holds both for 24 species, taken from the same source tables at the same moisture content — which is enough to compare species instead of quoting one from memory.
What the two numbers are
Modulus of elasticity (E, here in GPa) is the slope of the stress–strain line in bending. It says nothing about how much load a piece can take, only how far it moves under a given one. Every deflection formula in the beam calculator divides by it, so doubling E halves the deflection at the same section and span.
Modulus of rupture (MOR, here in MPa) is the bending stress at which a small clear specimen breaks. Turning it into a safe load takes the section modulus and a factor of safety, so it sits one step further from anything you can read off a span table.
The two do not rank alike. Teak and Spruce (Sitka) are within 1% of each other on stiffness — 10.7 against 10.8 GPa — but 43% apart on strength, 100.7 against 70.3 MPa. Choose a species for "strength" and you have not necessarily chosen one that feels stiff, and the reverse holds too.
The full ranking
Sorted by stiffness, which is the order a deflection calculation would put them in. Each name links to the page that carries the source table and the original inch–pound figures.
| Species | E (GPa) | MOR (MPa) | Density (kg/m³) |
|---|---|---|---|
| Ipe | 21.6 | 175.1 | 1000 |
| Hickory | 14.9 | 139.3 | 820 |
| Birch (Yellow Birch) | 13.9 | 114.5 | 690 |
| Fir (Douglas) | 13.4 | 85.5 | 530 |
| Larch | 12.9 | 89.6 | 580 |
| Maple (Hard Maple) | 12.6 | 108.9 | 705 |
| Pine (Southern Yellow) | 12.3 | 88.3 | 550 |
| Oak | 12.3 | 104.8 | 750 |
| Rosewood (East Indian) | 12.3 | 116.5 | 850 |
| Ash (White) | 12.0 | 103.4 | 670 |
| Beech (American) | 11.9 | 102.7 | 720 |
| Walnut (Black) | 11.6 | 100.7 | 660 |
| Hemlock (Western) | 11.2 | 77.9 | 470 |
| Poplar (Yellow) | 10.9 | 69.6 | 420 |
| Spruce (Sitka) | 10.8 | 70.3 | 430 |
| Teak | 10.7 | 100.7 | 630 |
| Mahogany (Honduran) | 10.3 | 79.3 | 550 |
| Cherry (Black) | 10.3 | 84.8 | 560 |
| Basswood | 10.1 | 60.0 | 420 |
| Cypress (Bald) | 9.9 | 73.1 | 480 |
| Redwood | 9.2 | 68.9 | 420 |
| Cedar (Western Red) | 7.7 | 51.7 | 370 |
| Cedar (Eastern Red) | 6.1 | 60.7 | 470 |
| Balsa | 3.4 | 21.6 | 160 |
Stiffness runs 6.41× from Ipe at 21.6 GPa down to Balsa at 3.4 GPa. Strength runs 8.09× over a wider band, from Ipe at 175.1 MPa to Balsa at 21.6 MPa. Rank them one way and then the other, and the orders separate: Fir (Douglas) is 26% stiffer than Teak and 18% weaker. A species can be chosen for the load it survives and still be a poor one for the deflection it allows.
Weight is not the ranking either. Among the lighter half of the table the stiffest species is Fir (Douglas), at 13.4 GPa and 530 kg/m³; the densest species listed is Ipe, at 21.6 GPa and 1000 kg/m³. "Pick the heaviest wood" is a rule of thumb, not a calculation.
What the spread is worth in a beam
Change only the species, holding section, span and load fixed, and the deflection ratio between two species is exactly the ratio of their E. On a nominal 2×10 — 38.1 × 234.95 mm actual — spanning 3657.6 mm under 2 kN/m, simply supported:
- Ipe — 5.2 mm (span/700)
- Oak — 9.2 mm (span/397)
- Balsa — 33.5 mm (span/109)
Section is the other lever, and it enters as the cube of depth. The same oak in a 2×6 deflects 4.76× what the 2×10 does, and a 2×8 deflects 2.08×. The species range (6.41×) is wider than the whole 2×6 to 2×10 step (4.76×), so species is worth roughly a lumber size or two — not a rounding error, but also not the lever to reach for first.
What these numbers are not
- They are clear, straight-grained, small-specimen values at 12% moisture content, from Table 5–3b and Table 5–5b. A full-size joist has knots, slope of grain and checking; a design value starts from these numbers and reduces them.
- They are species averages. Two boards of the same species differ by more than the precision printed here, so one sample neither confirms nor contradicts a row.
- They are not a code check. The beam calculator prints the same arithmetic this article does, and carries the same warning about itself: it is geometry and elastic modulus, not an approval.
- Turning MOR into a permissible load needs a factor of safety, a load-duration factor and a size factor. None of those are in this database, and this article does not supply them.
Choosing with the table
- Pick the species for what the table cannot tell you: decay resistance, movement in service, how it takes a finish, and what the yard actually stocks in the length you need.
- Pick the depth for stiffness. It is the lever whose effect you can predict before you order anything.
- Use the table to check that the species you picked has not quietly halved the stiffness you designed for.
- Treat the span-to-deflection ratios as reference lines, not rules. Which one applies is set by the code governing the building and by what the floor carries.
Each species page carries the same values with its source table and the original inch–pound figures, the lumber size pages carry what the nominal sizes actually measure — which is where the effective depth comes from — and the wood index groups the species by hardwood, softwood, exotic and engineered stock.