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For straightening a timber edge, a sole around 500–600 mm (20–24 in) is usually the best choice. That length gives the plane enough bearing surface to bridge hollows while the cutter removes the high spots. A shorter plane is easier to control and costs less, but it is more likely to follow a wavy edge instead of correcting it.
The traditional tool for this job is a jointer plane, often called a No. 7 or No. 8. A No. 7 is roughly 560 mm (22 in) long; a No. 8 is commonly about 610 mm (24 in). Either can produce a straight edge. The longer No. 8 is not automatically better—it is heavier, more tiring, and less convenient on narrow or shorter boards.
The basic rule for sole length
A plane straightens an edge by riding over high areas and cutting them down. Its sole acts as a reference. If the sole is longer than the hollow in the timber, the plane bridges that hollow and cuts the ends of the high spots. With repeated passes, the high areas come down until the edge is straight.
If the plane is too short, its front and rear sections can sit inside the hollow. The cutter then follows the existing curve rather than correcting it. This is why a 230 mm (9 in) smoothing plane is a poor first choice for making a long, straight edge, even though it can leave a finer surface.
As a practical guide:
| Sole length | Best use | Main limitation |
|---|---|---|
| 200–250 mm (8–10 in) | Local correction, final smoothing, small parts | Too short for reliably straightening long edges |
| 350–400 mm (14–16 in) | Jack-plane work and general preparation | May follow long hollows |
| 500–560 mm (20–22 in) | Most edge-jointing and straightening | Heavier and slower in tight spaces |
| 600–610 mm (23–24 in) | Long boards and demanding edge joints | More effort, cost, and sharpening demand |
Choosing between 22 and 24 inches
For most furniture work, a 22-inch jointer plane is the sensible middle ground. It is long enough to straighten common boards, but easier to push than a 24-inch plane. It also fits more comfortably on a typical bench and is less awkward when working on a board only 1–2 m (3–6 ft) long.
Choose a 24-inch plane when you regularly straighten long stock, wide door components, workbench parts, or timber with substantial bowing. The extra 50 mm does help, but the improvement is incremental rather than dramatic. A well-tuned 22-inch plane used with accurate technique will outperform a poorly sharpened 24-inch plane.
For occasional repairs or a small workshop, a No. 7 jointer hand plane is generally the safer purchase. A No. 8 makes more sense if you already know you need its extra length and weight.
Match the plane to the board and defect
Sole length is only part of the decision. On a 900 mm (36 in) board, a 400 mm jack plane may be perfectly adequate. On a 2.4 m (8 ft) board, the same plane can leave a gentle hollow between the ends. The defect matters as well: a short, local hump does not require a long plane, while a continuous bow benefits from the longest practical sole.
Check the edge with a straightedge before planing. Mark high spots with pencil, then take controlled cuts. If the edge is badly bowed, use a jack plane with a slightly cambered iron to remove waste quickly, followed by the longer jointer plane. A jointer plane with a narrow, square iron is better for establishing the final straight edge.
For boards under about 1.2 m (4 ft), a 14–16 inch jack plane can often do the entire job. It is a cheaper and more versatile option, especially if you also need to flatten faces or fit doors. Look at No. 5 jack planes if you want one general-purpose plane rather than a dedicated jointer.
Width, weight, and control
A longer sole does not make the plane automatically more accurate. The sole must be reasonably flat, the iron must be sharp, and the blade must be set for a controlled cut. For edge jointing, a plane around 50–60 mm (2–2 3/8 in) wide is comfortable. Wider planes cover more surface but increase weight and can be tiring on hardwood.
Weight helps when removing material from dense timber, but it does not replace a sharp edge. A heavy plane can also make it harder to feel when the cut changes direction. If you work mostly softwood, a lighter 22-inch plane may be more pleasant than a very heavy cast-iron model.
Do not judge a used plane solely by its stated size. A badly damaged sole, loose frog, distorted mouth, or cracked casting can turn a bargain into a restoration project. On a new plane, check that the sole is reasonably flat and that the lateral adjustment moves the blade predictably. The cutter should project evenly across its width.
Technique matters as much as length
Support the board firmly and keep the edge accessible. Start with the cut aimed at the high areas rather than trying to take a full-length shaving immediately. Use shorter strokes over high spots, then lengthen the stroke as the edge improves. Finally, take light full-length passes to blend the surface.
Keep the plane square to the face unless you deliberately want a bevel. A slight skew can reduce cutting resistance, but too much skew changes the effective sole length and can make the edge harder to control. Check progress with a straightedge and winding sticks rather than relying on appearance alone.
Grain direction is another common failure point. Reversing grain can cause tear-out even when the edge is straight. Reduce the cut, sharpen the iron, or work from the opposite end if the grain allows. A high cutting angle or a closely set mouth can help difficult timber, but neither fixes a blunt blade.
The best choice for most buyers
Buy a 20–22 inch jointer plane if your main task is producing straight edges for boards, shelves, and cabinet parts. Buy a 14–16 inch jack plane if you need one cheaper, more flexible tool and normally work on shorter stock. Choose a 24-inch plane only when long timber and demanding joinery justify the extra effort.
If budget is limited, spend first on a sound, sharp plane and a reliable straightedge. A good hand-plane sharpening kit can improve results more than moving from a 22-inch sole to a 24-inch one. For occasional edge straightening, borrowing or buying a used jointer plane is also reasonable, provided the defects are serviceable.
For a dedicated setup, pair the jointer with a long straightedge, a sturdy bench, and a shorter plane for local corrections. That combination gives better control than relying on one oversized plane for every stage of the work.