Why Jigsaw Blade Length Matters More Than You Think
Pick up a jigsaw blade, and the first thing you notice is length — the distance from the square-cut T-shank (the part that slots into your jigsaw) to the tip of the blade. You might think any blade longer than your workpiece thickness would work. But blade length controls three critical factors: maximum cutting depth, cut quality, and blade stiffness. Choose the wrong length, and your cuts wander, your saw binds, or you can’t cut at all.
A 50mm blade cuts 10mm deep. A 150mm blade cuts 75mm+ deep. But length isn’t just about depth — a blade that’s too short for the job will bend and deflect. A blade that’s too long for the work gets stiff and hard to control on curves. This guide walks you through the practical maths of blade length, shows you the standard sizes available in UK shops, and tells you exactly which blade to reach for based on what you’re cutting.
The Fundamental Rule: 25mm Longer Than Material Thickness
Why This Rule Exists
Here’s the physics: only the vertical portion of the blade (the part between the workpiece top and bottom) does the cutting. The T-shank doesn’t cut. The part of the blade inside the jigsaw housing doesn’t cut. So if you’re cutting a 20mm thick board, you need:
- 20mm of blade inside the material (doing the cutting)
- A minimum of 5mm of blade above the workpiece (holding stability)
- Some blade length in the jigsaw housing (mechanical requirement)
In practice, this works out to a simple rule: buy a blade at least 25mm longer than your material thickness.
What Happens If You Ignore This Rule
Blade too short: The blade doesn’t protrude far enough through the workpiece. The upper support arm (the jigsaws’s blade guide) loses grip on the blade, and it starts to bow sideways. Your cuts wander left and right, quality plummets, and binding increases. You’re fighting the saw.
Blade too long for the application: The long unsupported length above the workpiece flexes and vibrates. Cuts become rough and chattered. For intricate curves, a long blade is too stiff and won’t turn tight radii. You have to fight the blade’s natural stiffness.
The sweet spot: A blade 25mm+ longer than the material thickness gives maximum stiffness (minimizes deflection), maximum control, and the cleanest cuts.
Standard Jigsaw Blade Lengths in the UK Market
| Blade Length (mm) | Approx Cutting Depth (mm) | Best For | Common TPI Range | Availability |
|---|---|---|---|---|
| 50 | ~10 | Thin veneers, edge banding, foils | 18–30 TPI | Specialty sets only |
| 65 | ~15–20 | Thin plywood, 12mm boards, soft metals | 10–20 TPI | Less common, specialty suppliers |
| 75 | ~20–25 | Standard plywood, hardboard, thin hardwood | 6–18 TPI | All major brands |
| 100 | ~35–40 | 25–30mm solid timber, thick plywood, composite boards | 4–18 TPI | All major brands (most popular) |
| 125 | ~55–60 | 50mm+ hardwood, thick MDF, exotic timbers | 4–10 TPI | All major brands |
| 150 | ~70–75 | 75mm+ timber, thick composite materials, industrial work | 4–6 TPI | Premium sets, specialist suppliers |
Why 100mm Is the Industry Standard
The 100mm blade (3.9 inches, sometimes labelled as 4 inches in older literature) is the workhorse. It cuts 35–40mm deep — thick enough for most UK structural timber (25–30mm joinery stock, 38mm floorboards, 50mm decking edges). It’s stiff enough for fast, straight cuts yet still flexible enough for tight curves if you use an HCS blade. Every major brand stocks 100mm in multiple TPI variants. If you’re buying your first set, 100mm is your baseline.
Practical Length Selection by Material Thickness
Cutting Thin Materials (under 15mm)
Examples: Veneers, edge banding, 6mm plywood, thin acrylic, sheet metal, leather
Best blade length: 65mm or 75mm
Why: A 100mm blade is overkill and creates too much unsupported length above the workpiece. You lose control on curves and get vibration chatter on straight cuts. A 75mm blade (20–25mm cutting depth) gives you 3–4x the material thickness — plenty of margin and good stiffness.
Pro tip: On very thin veneers (under 3mm), a 50mm blade designed for fine detail work is worth seeking out. It’s specialty equipment but gives superior cut quality on delicate stock.
Cutting Standard Thickness (15–35mm)
Examples: Plywood (18mm, 25mm), MDF, hardboard, softwood framing (25mm), hardwood boards (20–30mm), worktop edges
Best blade length: 75mm or 100mm
Why: A 75mm blade (20–25mm cutting depth) works for 20mm boards but is marginal for 30mm+ timber — you’ll be cutting closer to the bottom limit of the blade. A 100mm blade (35–40mm cutting depth) is the comfortable choice. You get 25mm+ extra length, excellent stiffness, and can confidently cut anything up to 35mm. This is the UK standard for general carpentry.
Pro tip: For plywood curves where precision is critical (cabinetry, puzzle cuts), use a 75mm blade — it flexes more and follows curves better than the stiffer 100mm. Trade some speed for better curve control.
Cutting Thick Materials (35–75mm)
Examples: Hardwood blocks, thick composite boards, 50mm decking, 50mm+ laminated timber, industrial MDF
Best blade length: 125mm
Why: A 100mm blade can technically cut 40mm depth, but you’re cutting too close to the blade tip. You lose stiffness and curve control. A 125mm blade (55–60mm cutting depth) gives you 25mm+ margin on 50mm timber and cuts with excellent stiffness. For hardwoods where every cut shows, the extra stiffness of a 125mm blade produces visibly cleaner results than a 100mm blade.
Common mistake: Using a 100mm blade on 50mm hardwood because the math says it should work (100 – depth of shank = ~40mm cutting depth). In practice, you’re working at the edge of the blade’s capability. Use 125mm and work comfortably.
Cutting Very Thick Materials (75mm+)
Examples: Thick composite timbers, double-thickness boards, industrial assembly
Best blade length: 150mm
Why: A 150mm blade cuts 70–75mm deep — perfect for one-pass cutting through 75mm stock. You get maximum stiffness and speed.
Availability note: 150mm blades are less common in standard sets. You may need to buy individual blades from specialty suppliers. Most DIYers and tradespeople never need them because 75mm+ cutting is specialist work (heavy fabrication, architectural timber, lamination work).
Blade Length and T-Shank Sizing
Understanding T-Shank Depth
The T-shank is the square-cut tang that slots into your jigsaw. It’s standardized at roughly 20mm deep into the jigsaw housing (varies slightly by manufacturer). This means:
- A 75mm blade: ~20mm in the jigsaw, ~55mm of effective blade length outside
- A 100mm blade: ~20mm in the jigsaw, ~80mm of effective blade length outside
- A 125mm blade: ~20mm in the jigsaw, ~105mm of effective blade length outside
When calculating cutting depth, think of it as: Total Blade Length minus Shank Depth minus Material Thickness = Spare Margin. You want spare margin of at least 5mm for stability.
Are All T-Shanks Identical?
Modern T-shank blades are universal — they fit any T-shank jigsaw (Bosch, DeWalt, Makita, Milwaukee, Festool, etc.). The shank depth varies slightly (18–22mm depending on manufacturer), but blade lengths are standardized by total length, not by effective cutting length. A 100mm Bosch blade and a 100mm DeWalt blade are both approximately 100mm total, though the exact shank depths might vary by 1–2mm.
If you’re mixing brands: No problem — all modern T-shanks work with all modern jigsaw models. But if you have an older U-shank jigsaw (pre-2000s), you’ll need U-shank blades, which are increasingly hard to find. Consider upgrading to a modern T-shank jigsaw.
Blade Length, Stiffness, and Cut Quality
The Stiffness Trade-Off
A longer blade is stiffer — up to a point. Here’s why:
- Short blade in deep material: The unsupported length above the workpiece is long relative to the blade thickness. The blade bends sideways under cutting pressure. Your cuts wander.
- Ideal blade for the material: The unsupported length above the material is short (25–40mm). The blade is stiff and resists sideways deflection. Cuts are straight and clean.
- Long blade in shallow material: The unsupported length is very long. The blade becomes too stiff to follow tight curves. You’re fighting the blade’s natural inflexibility.
Real-world example: Cutting a 20mm board:
- 100mm blade: ~80mm unsupported length above the board. Too much flex, cuts wander.
- 75mm blade: ~55mm unsupported length. Good stiffness, stable cuts.
- Result: Choose the 75mm blade for thin material despite the longer blade (100mm) being “available”. Shorter is better here.
Stiffness vs Flexibility for Curves
Shorter blades are more flexible, which is good for tight curves. Longer blades are stiffer, which is good for straight cuts. This is why curve work (intricate joinery, inlays, puzzle cuts) often uses shorter blades than the material thickness strictly requires:
- Cutting 25mm hardwood with tight curves: You’d theoretically use a 75mm blade (25mm material + 25mm margin + 25mm in jigsaw). But for intricate work, use a 65mm blade for extra flexibility, accepting that your margin is only 15mm instead of 25mm.
- Cutting 25mm hardwood straight (frame pieces, edges): Use a 100mm blade. The extra stiffness produces straighter edges.
Choose blade length based on the nature of the cut, not just the material thickness.
Maximum Cutting Depth by Blade Length (UK Reference Table)
| Blade Length | Approx Max Depth | Recommended Max Material | Minimum Margin | Typical TPI Options |
|---|---|---|---|---|
| 50mm | ~10mm | 5mm (veneers, edge banding) | 5mm | 20–30 TPI |
| 65mm | ~15–20mm | 12mm (thin plywood, soft metals) | 5–10mm | 10–20 TPI |
| 75mm | ~20–25mm | 20mm (standard ply, hardboard, thin hardwood) | 10–15mm | 6–18 TPI |
| 100mm | ~35–40mm | 30mm (solid timber, thick ply, composite) | 10–20mm | 4–18 TPI |
| 125mm | ~55–60mm | 50mm (thick hardwood, industrial MDF) | 15–20mm | 4–10 TPI |
| 150mm | ~70–75mm | 75mm (thick composites, specialist work) | 10–15mm | 4–6 TPI |
Read the table this way: For 30mm solid timber, you want a 100mm blade (recommended max material = 30mm). For 50mm timber, jump to 125mm. For 20mm plywood, a 75mm blade is comfortable.
Blade Length and Pendulum Action
How Pendulum Affects Blade Length Choice
Many modern jigsaws have pendulum action — the blade swings slightly forward and backward during the cut. This speeds up cutting (especially in wood) by breaking chips ahead of the main cutting edge.
Pendulum action works best with longer blades because the swing motion is more stable with greater unsupported length. This is another reason to use 100mm+ blades for general work — the longer blade works better with pendulum cutting.
On shorter blades (65–75mm), pendulum action can cause chatter and instability. You may need to reduce pendulum level or disable it entirely when using shorter blades on thin materials.
Check your jigsaw manual for pendulum advice. Most models have 3–4 pendulum settings. For thin work, use low pendulum or off. For thick timber with a long blade, use high pendulum for faster cutting.
Blade Length by Tool Type and Brand
Most UK brands stock 75–100mm as standard. Here’s what you’ll typically find:
| Brand | Most Common Lengths | Specialty Lengths |
|---|---|---|
| Bosch | 75, 100, 125mm | 50mm (fine detail), 150mm (heavy duty) |
| DeWalt | 75, 100mm | 125mm in some sets |
| Makita | 75, 100mm | 65mm (specialty), 125mm (premium sets) |
| Milwaukee | 75, 100mm | 125mm in contractor sets |
| Ryobi | 100mm (most sets) | 75mm occasionally |
If you need 125mm or 150mm blades, buy from specialty suppliers or directly from Bosch — they’re not standard in budget sets.
Practical Tips for Blade Length Selection
Tip 1: Measure Your Workpiece First
Before selecting a blade, measure the thickness of what you’re cutting. Then add 25mm. That’s your target blade length.
- 18mm plywood? 18 + 25 = 43mm → Use a 75mm blade (nearest standard size above 43)
- 30mm hardwood? 30 + 25 = 55mm → Use a 100mm blade
- 50mm timber? 50 + 25 = 75mm → Use a 125mm blade
Tip 2: Err on the Side of Longer
If you’re between sizes, choose the longer blade. A 100mm blade can cut 30mm material, but it’s working at the edge. A 125mm blade is overkill for 30mm but cuts with noticeably better stiffness and quality. The extra cost (£1–£2 per blade) is worth the improvement in cut quality.
Tip 3: For Curves, Go Shorter if Possible
If your cut includes tight curves (radius under 50mm), consider dropping one blade size down for better flexibility. A 75mm blade curves better than 100mm, even if it’s technically longer than needed by the 25mm rule.
Tip 4: Keep Multiple Lengths in Your Kit
Buy a basic set with 75mm or 100mm, then add individual 65mm or 125mm blades as your work demands them. You don’t need every length, but having 2–3 standard lengths covers 95% of UK carpentry work.
Tip 5: Check the Blade Closely After Buying
Measure the blade end-to-end with a ruler. Some manufacturers are loose with “100mm” — you might get 95mm or 105mm. If you’re working near the limits (cutting 35mm material with a “100mm” blade that’s actually 95mm), those 5mm matter. Check before relying on a blade for critical work.
Blade Length and Jigsaw Model Compatibility
Do All Jigsaws Accept All Blade Lengths?
Yes and no. All modern T-shank jigsaws accept any T-shank blade length (50–150mm). But some older models or budget DIY jigsaws have blade guide designs that don’t handle very short (50mm) or very long (150mm) blades smoothly — the guides bind or don’t grip properly.
Safe assumption: Any blade between 65mm and 125mm works with any T-shank jigsaw. If you’re using 50mm or 150mm blades, check your jigsaw manual to confirm compatibility.
Blade Guides and Maximum Length
The blade guide (the metal block above and below the blade inside the jigsaw) keeps the blade vertical during cutting. If a blade is too long for your jigsaw’s design, the guide may not grip properly at the top, causing flex and poor cuts. This is rare with modern design, but it’s worth checking.
Check your jigsaw manual for: Recommended blade length range, maximum cutting depth (which tells you implicitly which blade lengths are appropriate), and any warnings about specialty blade lengths.
Blade Length and Cost
Longer blades cost slightly more because they use more material:
- 75mm blade: £0.50–£2.00 (HCS) / £2–£5 (BIM)
- 100mm blade: £0.50–£2.50 (HCS) / £2–£6 (BIM)
- 125mm blade: £1–£3 (HCS) / £3–£7 (BIM)
- 150mm blade: £1.50–£4 (HCS) / £4–£10 (BIM)
The price difference between 75mm and 125mm is typically £0.50–£1 per blade. Not a reason to compromise on the right length. Buy what the job needs.
Frequently Asked Questions
What happens if I use a blade that’s too short for the material?
The blade will flex and bend sideways under cutting pressure. You’ll see your cuts start to wander left and right (called deflection). The blade may bind and stall. For thick material, a blade that’s too short is essentially unusable — the cut quality is too poor. Always use the 25mm margin rule.
Can I use a 150mm blade on thin material (10mm)?
Technically yes, but it’s not ideal. The blade is too stiff and will cause chatter and rough cuts on thin material. You’ll also have massive unsupported length above the workpiece, making it hard to control curves. Use a 50–65mm blade for thin material and save the 150mm for thick work.
Why are some blades labeled in inches and others in millimetres?
Older UK and US blades used inches (2-inch, 3-inch, 4-inch, 5-inch, 6-inch). Modern blades use millimetres. The conversions are approximate: 2″ ≈ 50mm, 2.6″ ≈ 65mm, 3″ ≈ 75mm, 4″ ≈ 100mm, 5″ ≈ 125mm, 6″ ≈ 150mm. If you have old blades, convert to mm to understand their cutting depth.
Is there a standard jigsaw blade length I should always buy?
100mm is the industry standard. It covers 25–35mm material comfortably and is the most versatile size. If you’re buying one set, 100mm is your foundation. Add 75mm for thin work and 125mm for thick work as needs arise.
How do I know the exact cutting depth of a blade?
Subtract approximately 20mm (the shank depth in the jigsaw) from the total blade length. That’s the maximum possible cutting depth. For 75mm: 75 – 20 = 55mm maximum. But remember, you want 25mm margin, so effective working depth is 55 – 25 = 30mm. This is conservative and safe.
Can I use a short blade on deep material if I do multiple passes?
You can, but it’s inefficient and frustrating. Doing 4–5 passes with a 65mm blade on 50mm material takes forever and accumulates heat (risk of the blade burning out). Buy the right blade length for the job — 125mm in this case — and cut once.
Do premium brand blades cut deeper than budget blades?
No — a 100mm Bosch blade and a 100mm supermarket blade both cut to the same depth. The difference is edge life and cut quality, not depth. Blade length determines depth, not brand.
What’s the point of 150mm blades if they’re so rare?
They’re specialist tools for heavy-duty industrial work — thick composite materials, laminated timber structures, demolition. For regular UK trade work (carpentry, joinery, fit-out), you rarely need them. Stick with 75–125mm and you’re covered.
Should I buy a set with different blade lengths?
Yes. A 10–30 piece set typically includes both 75mm and 100mm blades in various TPI, covering most work. Don’t buy a set that’s only 100mm — you’ll need 75mm for thin plywood and other delicate materials. Multi-length sets are worth the extra cost.
Summary: Choosing the Right Blade Length
The 25mm Rule: Buy a blade at least 25mm longer than your material thickness. This ensures stiffness, stability, and clean cuts.
Standard Lengths: 100mm is the workhorse. 75mm handles thin material. 125mm handles thick material. Most UK work uses these three sizes.
For General Carpentry: Start with a 100mm set. Add 75mm for thin plywood. Add 125mm only if you regularly cut 50mm+ timber.
For Intricate Curves: Go one size shorter than the 25mm rule suggests (use 75mm on 20mm material instead of 100mm) for better flex and curve control.
For Production/Heavy Use: Invest in 125mm premium BIM blades. The extra stiffness and edge life justify the cost on thick hardwoods.
Blade length is one of the most straightforward aspects of jigsaw selection. Measure your material, add 25mm, and pick the standard size that’s closest above that number. You’ll cut faster, cleaner, and more safely than working with the wrong blade length. Buy blades to suit the work, not the other way around.
Related Guides
- Jigsaw blade compatibility hub — Brand and model matching
- Jigsaw blade materials explained — HCS vs BIM vs HSS vs TCT
- TPI guide — Teeth per inch and cutting speed
- Best jigsaw blade sets (2026) — Bosch, DeWalt, Milwaukee, Makita recommendations
- Blades for wood — Optimal TPI and tooth design for timber
- Blades for tiles — TCT and carbide grit for ceramics and stone
Where to Buy Jigsaw Blades
Once you know what length and type you need, here are our recommended sources:
Buy Bosch Jigsaw Blade Sets on Amazon
Buy DeWalt Jigsaw Blade Sets on Amazon
Buy Makita Jigsaw Blade Sets on Amazon
For the full UK buying guide, see our Where to Buy Jigsaw Blades guide.
