Log Splitter Tonnage Guide UK: What Size Do You Need?

What the tonnage badge really means

A splitter's tonnage is the maximum force the ram can push with. It's set by two things: the hydraulic pressure the pump and relief valve allow, and the area of the ram piston. Force = pressure × piston area. That simple formula explains a lot.

Take Forest Master's published figures. Its electric range quotes 5 tonnes at 400 bar, 7 tonnes at 500 bar and 8 tonnes at 550 bar. Working backwards, all three imply a ram roughly 40–43mm across (my calculation). In other words, on these machines the step from 5 to 7 tonnes comes mainly from higher hydraulic pressure, not a bigger cylinder.

The same maths is a useful check on any spec sheet:

My calculation: force = pressure × π × (bore ÷ 2)², converted to tonnes-force. Published pressures may be rounded.

The takeaway: badges are rounded, sometimes generously, and two machines with the same badge can perform differently. The badge also says nothing about speed, wedge shape or log capacity, which often matter more in daily use.

Tonnage and log diameter

More diameter generally needs more force, but less than most buyers think. Forest Master goes as far as calling the idea that you need a more powerful splitter for larger diameters "a fallacy". Its point is that "the hardest part of the log is in the centre" and that "you should be aiming for just off-centre of the log". Splitting slabs off the edge of a big round takes much less force than driving straight through the heart.

In practice, a splitter's maximum log diameter is limited as much by its frame, guard and wedge as by its force. Here's what manufacturers actually rate their machines for:

Specs from manufacturer and retailer listings, checked October 2026. *Forest Master quotes 400mm on its product pages and up to 500mm in the FM10 manual; maximum diameters apply with the safety guard fitted.

Two patterns stand out. First, the 250mm ceiling on most 4–6 tonne electric machines comes from the frame, not just the force. Second, the jump to 7–8 tonnes is where rated diameter rises to around 400mm. Look at the diameter rating, not just the badge.

Timber species

Species can matter more than diameter. Champion Power Equipment's buying guide tells buyers to work out tonnage from "the hardest wood" they expect to split, not the average. From manufacturer guidance and owner reports, here's how common UK firewood species tend to behave:

A practical guide compiled from manufacturer advice and owner reports, not lab cleavage tests. Individual logs vary a lot.

Tree history matters too. One experienced US owner observed that "the trunks of most big, old yard trees are very difficult to split", while trees grown in dense stands tend to have cleaner, straighter grain. Garden and hedgerow trees grown in the open are usually knottier and twistier than forestry timber.

Grain and knots

A log splits along its grain. Where the grain runs straight, very little force is needed once the wedge starts a crack. Interlocked, spiral or wavy grain, and especially knots, make the fibres hold together across the split, and force requirements jump. Practical tips from manufacturers and owners:

• Orient the knot. Forest Master's manual recommends placing logs "that have a visible knot, so that the knot is vertical", so the wedge splits through it in line rather than across it.
• Work from the edges. On stubborn rounds, take slabs off the outside first. Elm specialists on Arbtalk advise splitting off the sapwood first and working "in to the Center".
• Use the cracks. Husqvarna advises you to "split along the grain, aiming for cracks" already present in the end of the log.
• Choose the right wedge. Forest Master notes that a more acute blade can "get lost inside" big logs, and that its 8-ton FM16 uses a more obtuse blade for tough, fibrous wood. Twin-blade designs split from both ends, so a knot at one end doesn't stop the split.
• Don't hold the pressure. Most manuals say never hold full pressure for more than about five seconds. Release, rotate the log and try again.

If a knotty log won't go, more tonnage isn't always the answer. Repositioning the log, or cutting it shorter, often works better. If your splitter seems weaker than it should be on every log, see our troubleshooting guide for slow rams and leaks.

Moisture: green or seasoned?

This is where the experts disagree, and the answer depends on the species and the type of splitter:

My take: on hydraulic splitters, split green where you can, especially stringy or interlocked species. On impact tools (axes, mauls, slide-hammers and kinetic splitters), seasoned or frozen wood usually breaks more cleanly. Either way, logs must reach 20% moisture or less before burning; in England, wood sold in small quantities must be certified "Ready to Burn" to that standard.

Shop firewood moisture meters Shop safety goggles

Log length and wedge design

Longer logs take more force, because the wedge has to drive the split further before it runs through. They also need a longer ram stroke. That's why small machines limit length as well as diameter: 300–370mm on 4–5 tonne electrics, 450–550mm on 6–8 tonne machines, and up to 1.1m on large vertical petrol splitters.

Measure your stove first. Most stoves take logs of 25–40cm, so a 370mm-capacity machine is often enough. Choosing a longer capacity than you need costs money and floor space, and won't add useful force.

Wedge design changes how far tonnage goes. A 4-way wedge produces four pieces per stroke but needs more force per push. Twin-blade designs split from both ends. A tall, obtuse wedge copes better with fibrous wood. Compare wedges alongside tonnage.

Choosing your tonnage: the matrix

Start with your typical log diameter, then move one band up for each "harder" factor that applies to most of your wood: tough species, knotty or twisted grain, or the wrong moisture state for your splitter type.

Garden-Review guidance, built from manufacturer maximum-diameter ratings and the species and grain factors above. It's a starting point, not a guarantee. Always check the machine's own rated maximum diameter and length.

Then use the power source to narrow your choice. 4–8 tonnes is the domestic electric splitter range from a 13A socket. Above that, you're usually into petrol splitters. For kindling and occasional small logs, see manual splitters explained.

Example splitters by tonnage band

Research-based examples covering each band, all covered in more detail in our other buying guides. Prices change often, so check the live listing.

For ranked picks across every type, see Best Log Splitters UK 2026 or browse our log splitter reviews.

Tonnage buying checklist

Frequently asked questions

What tonnage log splitter do I need?

For straight-grained logs up to about 25cm, 4–5 tonnes is usually enough. For mixed hardwood up to 30–40cm, choose 6–8 tonnes. Knotty or tough species such as elm and beech, and rounds over 35cm, call for 10–15 tonnes or more. Always check the machine's rated maximum diameter.

Is a 5 ton log splitter enough?

For softwood and straight-grained hardwood up to about 25cm, yes. Forest Master describes 5 tonnes as entry-level and best for softwood, with hardwood requiring "more planning". If you split beech, elm, fruit wood or knotty logs regularly, 7–8 tonnes is a safer choice.

What size log can a 7 ton splitter split?

Typical 7-tonne electric splitters are rated for logs up to around 400mm diameter and 430–450mm long. That assumes reasonably straight grain; knotty or tough species may need splitting from the edge.

Which firewood is hardest to split?

Among common UK species, English elm, plane, hornbeam, fruit wood and large old open-grown trees are usually the hardest, because of interlocked or twisted grain and knots. Ash, birch and straight-grained softwood are the easiest.

Is green or seasoned wood easier to split?

It depends. Forest Master recommends splitting green wood on its hydraulic splitters, and stringy species get harder when dry. Champion and impact-tool makers find seasoned, brittle wood easier. As a rule: hydraulic splitters, split green; axes, slide-hammers and kinetic splitters, seasoned or frozen.

Does a bigger log need more tonnage?

Somewhat, but less than many people assume. The centre of a log is hardest to split, so working slabs off the edge reduces the force needed. A splitter's frame and wedge also limit diameter, so check the rated maximum log size.

More in this hub: Log Splitters hub · Log splitter buying guides · Choosing an electric splitter · Petrol log splitter guide · Manual splitters explained

Sources: Forest Master "Electric Log Splitter – What Tonnage Do I Need?" and replies, FM5/8/10 manual and comparison chart; Champion Power Equipment log splitter buying guide; Husqvarna firewood guide; manufacturer and retailer spec listings (Scheppach, The Handy, Konner & Sohnen, Sealey, SIP, Lumag, Forest Master); Mammoth Hire (Oxdale SE400 specs); Trade Tested NZ (Hyundai 25T specs); Arbtalk "Splitting Elm" thread; Hearth.com "What wood is the worst to split" thread. Checked October 2026.