Firewood Splitting Difficulty by Species: Hardness, Grain and What Needs a Wedge
Straight-grained species — ash, red oak, hard maple, cherry, most pine — split cleanly with a 4 to 6 lb splitting axe. Interlocked species — American elm, sweetgum, sycamore, blackgum — resist a maul entirely and want wedges, a hydraulic ram or a hard freeze. Janka hardness tells you almost nothing about splitting; grain straightness and stringiness tell you everything.
By the The Tool Wise Editorial Team
White ash, red oak and hard maple split so cleanly that a competent swing halves a 16 inch round in one. American elm, sweetgum and sycamore will absorb a full day of swinging and give you a pile of shredded, half-connected chunks.
The variable is not hardness. It's grain. Species with straight, parallel fibres part along the ray planes almost willingly; species with interlocked grain, where fibre direction alternates every few growth rings, have no continuous plane to part along and simply weave themselves back together around your bit.
The table below carries both figures so you can see how badly they correlate. Osage orange has a Janka figure roughly seven times that of aspen and splits more easily than elm, which is soft by comparison. Read the stringiness column, not the hardness column, when you're deciding what tool comes off the wall.
Why Janka is the wrong number for this job
The Janka test presses a steel ball halfway into a board and records the force. It measures resistance to denting and wear, which is genuinely useful for flooring and for guessing how fast a species will dull a bit.
Splitting is a completely different mechanism. You're not compressing wood, you're propagating a crack along the grain, and the resistance to that depends on how straight the fibres run, how strong the ray tissue is that binds them, and how much moisture is holding the cell walls plastic.
Hickory is the clean demonstration. It's one of the hardest common firewoods, near the top of the Janka range, and it splits beautifully because the grain runs dead straight. Elm sits far below it for hardness and is close to unsplittable by hand. Same physics, opposite outcomes.
Where Janka does earn its place: it predicts edge wear. A day of splitting osage orange, hickory or black locust will dull a bit noticeably, and a filing session is part of the job rather than an afterthought.
The species table
Split ratings run 1 to 5, where 1 falls apart looking at it and 5 needs a machine. Stringiness is separate and it's about what happens when the crack does start — some species part cleanly, others hold together on long fibres that have to be cut rather than split.
BTU figures are per full cord of seasoned wood at roughly 20 percent moisture. A full cord is 128 cubic feet stacked, which is a 4 by 4 by 8 foot rick. Seasoning months assume split, stacked, off the ground and top-covered in a reasonably breezy spot.
Species Janka (lbf) Grain Stringiness 1-5 Green split 1-5 Seasoned split 1-5 Tool that finishes it BTU per cord (million) Seasoning White ash 1320 Straight, even 1 1 1 4-6 lb splitting axe; the benchmark for easy 24 6-12 months Red oak 1290 Straight, open pored 1 1 2 5-6 lb splitting axe 24 12-18 months White oak 1360 Straight, tight 2 2 3 6 lb maul; wedges on anything over 20 in 26-27 18-24 months Sugar maple 1450 Straight to slightly wavy 2 2 3 6 lb maul 24 9-15 months Silver maple 700 Straight, soft 2 1 2 4 lb splitting axe 19 6-9 months Shagbark hickory 1880 Straight, dense 2 1 2 6 lb maul; expect to file the bit afterwards 27-28 12-18 months American beech 1300 Straight but tough rays 3 2 4 6-8 lb maul, wedges when dry 24 12-18 months Yellow birch 1260 Straight, fine 2 2 3 5-6 lb maul 23-24 9-12 months Black cherry 950 Straight, clean 1 1 2 4 lb splitting axe 20 6-9 months Black walnut 1010 Straight 2 1 2 4-5 lb splitting axe 20-22 9-12 months Black locust 1700 Straight, sometimes spiralled 2 2 3 6 lb maul; splits well but is brutal on edges 27 12 months Honey locust 1580 Straight to interlocked 3 3 4 6-8 lb maul plus wedges 26 12 months Osage orange 2620 Straight, extremely dense 2 2 3 6 lb maul; the hardest common firewood and still splits 32-33 12-18 months Mulberry 1680 Straight, slightly stringy 3 2 3 6 lb maul 25-26 12 months American elm 830 Heavily interlocked 5 5 5 Wedges, or a hydraulic splitter. Hand splitting is a losing bet 20 12-18 months Slippery (red) elm 860 Interlocked 5 4 5 Wedges minimum; hydraulic if there's any volume 19-20 12-18 months Sycamore 770 Interlocked, prominent rays 5 4 5 Wedges or hydraulic; splits better frozen than any other way 19-20 12 months Sweetgum 850 Interlocked, spiral 5 5 5 Hydraulic. Honestly, leave it in the woods 20-21 12-18 months Blackgum / tupelo 810 Severely interlocked 5 5 5 Hydraulic only, and it will still fight 20 12-18 months Eastern white pine 380 Straight, resinous 1 1 1 3-4 lb axe; a splitting maul is overkill 13-15 6-9 months Douglas fir 620 Straight 1 1 2 4 lb splitting axe 20-21 6-12 months Quaking aspen 350 Straight, soft, fibrous 3 2 3 4 lb axe; fibres hold on when dry 14-15 6-9 months Eastern red cedar 900 Straight, brittle 1 1 1 3-4 lb axe; splits almost on impact 18 6-9 months Sort mentally by the two split columns, not by Janka. Anything rated 5 in both should be wedged, frozen or run through a hydraulic ram, and anything rated 1 doesn't justify hauling out a maul. Two entries in that table are worth arguing about. White ash is often called the best firewood there is, and the reason is the combination in its row: easy split, high BTU, short seasoning, and it burns respectably at higher moisture than most species. If you're buying one cord, buy ash.
Sweetgum is the opposite recommendation and it's blunt. Unless you own a hydraulic splitter it produces the worst return on effort of any common hardwood, and the BTU figure isn't good enough to justify the fight. Cut it into short rounds and burn it whole in an outdoor pit, or pass on it.
Moisture state changes the answer completely
The same round can be easy in March and impossible in July. Water in the cell walls keeps the fibres plastic and lets a crack run; dry out an interlocked species and those woven fibres go leathery and grip.
Freezing does the reverse. Below about minus 7 C the free water in the cells turns to ice, the wood goes brittle, and species that shred at room temperature part with a crack. This is why old hands stack elm and sycamore for January.
State Approx moisture content Straight-grained species Interlocked species Practical call Fresh green, just felled 60-100 percent Easiest they will ever be; oak and ash almost fall apart Bad but survivable; elm at least holds together in one piece Split everything the week it comes down if you can Standing dead, bark off 25-40 percent Slightly harder than green, still straightforward Worse than green; fibres have already leathered Good wood, but split it before it dries further Three to six months air dried 30-45 percent Noticeably tougher; oak starts wanting a wedge Approaching hopeless by hand The awkward middle. Wedges earn their keep here Fully seasoned Under 20 percent Harder than green but clean; ash and cedar stay easy Worst case. Elm and gum are effectively hand-proof Split before this point, not after Frozen solid, below -7 C Any Splits explosively; watch for flying halves The single best window you will get. Elm becomes possible Save the stringy pile for a cold snap Punky, part rotted Variable and high Tears rather than splits; bit sinks and sticks Tears badly, no crack propagates at all Not worth the swing. Burn it in an outdoor pit or compost it Match your pile's row to your species group and decide the tool before the round is on the block. The frozen row is a scheduling instruction, not a curiosity. Knots, crotches and where to stop
Every rule above applies to clear wood. A knot is a branch base running perpendicular to the trunk grain, and it locks the two planes together like a dowel. A crotch — the Y where a limb leaves the trunk — is two grain directions interlocking over a foot or more of length.
Split around knots rather than through them. Aim the bit so the crack runs beside the knot and takes a slab off the outside; work inward from the bark in successive slabs rather than trying to halve the round. This is how you get through gnarled apple, big-limbed oak and anything with a lot of branch stubs.
Crotch wood is a different judgement. Split a crotch piece with the fork lying flat and the bit aimed into the fork line, not across it. If three good swings do nothing, that round is telling you it wants a wedge or a saw cut rather than more enthusiasm.
Wedges go in pairs. Start one in a crack at the edge, drive until it stops moving, start a second an inch or two along the same crack, and alternate. A single wedge driven to the head in a stubborn round is a wedge you'll be digging out with a second wedge.
- Rounds over about 20 inches: quarter them with wedges first, then finish the quarters with a maul.
- Rounds under about 10 inches of straight-grained species: a 4 lb splitting axe is faster than a maul and far less tiring.
- Set every round on a block, never on the ground. A round on soil absorbs the blow, and a miss goes into dirt and ruins the edge.
- An old tyre or a loop of chain around the round holds the pieces upright and roughly triples the number of splits per set-up.
- Overstrike protection matters more here than anywhere. A missed split drives the haft neck into the round, and that's what breaks handles.
Reading the BTU column without being robbed
A full cord is 128 cubic feet of stacked wood: 4 feet high, 4 feet deep, 8 feet long. Anything else is not a cord, whatever the advert says.
A face cord, rick or run is 4 feet high by 8 feet long by whatever the piece length happens to be. At the common 16 inch length that's about one third of a full cord. At 12 inches it's a quarter. Establish the piece length before you agree a price, because the same stack sold as a face cord can vary by a third in actual volume.
Moisture is the other lever. Wood at 50 percent moisture content delivers a fraction of its rated heat, because a substantial share of the energy goes into boiling off water before anything useful happens. Under 20 percent is the target. A cheap pin moisture meter, pressed into a freshly split face rather than an end grain, settles the argument in ten seconds.
Mixing species by burn phase is the practical move. Load pine or aspen to establish a fire fast, then oak, locust or hickory for the long overnight burn. Buying only high-BTU wood makes lighting the thing harder than it needs to be.
Wood that should not go in a stove
Some of this is about safety rather than difficulty, and it's worth stating.
Anything with a vine on it. Poison ivy, poison oak and poison sumac carry urushiol, urushiol survives combustion in smoke particles, and inhaling it causes a reaction in the airway that lands people in hospital. Check rounds for hairy vine remnants before they go anywhere near a fire.
Treated, painted or engineered material. Pressure-treated lumber, plywood, particle board, railway sleepers and anything with old paint release compounds you do not want in a room or in the ash you spread on a garden.
Driftwood off a salt shore. Chloride salts in the wood produce corrosive combustion products that eat stove liners and flue pipe.
Oleander and a small number of other toxic ornamentals. Rare in a woodpile, worth knowing about.
Green softwood in a slow overnight burn. Not toxic, just poor practice — unburned volatiles condense in a cool flue as creosote, and creosote is what chimney fires are made of.