How to Scale a Woodworking Plan Up or Down

Woodworking plans are drawn for a specific size — but the piece you need rarely matches exactly. Maybe the coffee table in a plan is 120 cm long and your room calls for 90 cm. Maybe the lumber sizes in an American plan don’t correspond to what’s sold at Bunnings. Knowing how to scale a plan correctly is one of the most practical skills a beginner can develop, and it’s less complicated than it looks once you understand a few rules.

Why You’d Need to Resize a Plan

The most common reasons to scale a woodworking plan are:

• Room dimensions — your space is smaller or larger than the plan assumes
• Lumber availability — the plan calls for a width you can’t source locally
• Material cost — building smaller to reduce timber use
• Proportional fit — matching an existing piece of furniture in the room

Whatever the reason, the approach matters. Scaling isn’t just multiplication — some dimensions scale freely, and others don’t.

Two Types of Scaling: Proportional vs Dimensional

Proportional Scaling

Proportional scaling means you multiply every dimension — length, width, and thickness — by the same factor. If your scale factor is 0.75, everything gets multiplied by 0.75. This keeps the piece looking right and ensures joints remain structurally valid.

To find your scale factor: divide the dimension you want by the dimension in the plan. If the plan shows a 1200 mm table and you want 900 mm, your factor is 900 ÷ 1200 = 0.75.

Dimensional Adjustment

Sometimes you only want to change one dimension — making a bookshelf taller but keeping the same depth and width, for example. This is dimensional adjustment, not full scaling. It works for simple pieces but can cause structural problems in more complex builds. If you only change the height of a cabinet without adjusting the shelf spacing or back panel, you may end up with disproportionate gaps or weak spots.

The Scaling Maths

The formula is straightforward:

New dimension = Original dimension × Scale factor

For a scale factor of 0.75 (75% of original): multiply each dimension by 0.75
For a scale factor of 1.25 (125% of original): multiply each dimension by 1.25

Work through the entire cut list before you buy any timber. Recalculate every part and write out a new cut list before you go to the hardware store.

Example: Scaling a Coffee Table

The table below shows how the key dimensions of a basic coffee table change at 0.75 and 1.25 scale factors. The original table is 1200 mm long × 600 mm wide × 450 mm tall.

The Critical Mistake: Scaling Joinery Breaks the Joint

This is where beginners go wrong. Joints are designed around specific proportions that have been tested for strength. If you scale a mortise-and-tenon joint proportionally, the tenon may become too thin to resist racking forces, or too thick to seat properly. Dowel joints scaled down may land on different wood fibres and lose their grip.

The rule: scale the overall dimensions of the piece, but leave joinery dimensions within engineering norms. A tenon should be roughly one-third the thickness of the mortised piece — that’s a structural requirement, not a stylistic one. If your scaled piece calls for a 6 mm tenon but standard practice is 8 mm minimum, use 8 mm and adjust the mortise accordingly.

The same applies to pocket hole screws, biscuits, and dowels — they come in fixed sizes. Scaling a plan down to 75% doesn’t mean your screws get smaller. Check that the original fastener sizes still make sense at your new dimensions.

Checking Against Available Timber Sizes

This is especially important in Australia, where most plans are written in imperial using North American lumber sizes. After scaling, check that your calculated dimensions correspond to timber you can actually buy. Common AU dressed pine sizes at Bunnings include:

• 19 × 38 mm
• 19 × 63 mm
• 19 × 90 mm
• 19 × 140 mm
• 35 × 35 mm
• 42 × 42 mm
• 42 × 90 mm
• 70 × 70 mm
• 90 × 90 mm

If your scaled calculation gives you a 53 mm × 53 mm leg (the 0.75 scale result in the table above), the nearest available size is 42 × 42 mm or 70 × 70 mm. Choose the size that keeps the structural intent of the original — and update the rest of the plan to match.

Step-by-Step Scaling Process

1. Identify your target dimension (the one that must change — usually length or height)
2. Divide the target by the original to get your scale factor
3. Multiply every part in the cut list by that factor
4. Check all joinery dimensions against structural minimums — do not scale these blindly
5. Round each calculated dimension to the nearest available timber size
6. Redraw or annotate the plan with the new dimensions before cutting anything
7. Re-check the overall piece makes visual sense at the new proportions

Quick Tips for Getting It Right

• Work in decimals, not fractions — convert fractions to decimals before multiplying, then convert back if needed
• Scale on paper first — make a rough sketch with the new dimensions before committing to a cut list
• Check visual proportion — a table scaled to 60% may look stubby; step back and assess before cutting
• Don’t scale hardware — hinges, drawer slides, and handles don’t scale. Buy them first, then build around them
• Update the materials list — a scaled-down piece uses less timber; recalculate board-feet or lineal metres to avoid over-buying

Scaling confidently opens up every plan you’ll ever find, regardless of what size it was originally designed for. Once you’ve done it a few times, it becomes second nature.

If you want hundreds of plans that are already professionally designed with full cut lists — and you can scale any of them using the method above — Ted’s Woodworking gives you 16,000 plans with step-by-step instructions. It’s the fastest way to build a project library as a beginner.

Related Guides

• How to Read a Woodworking Plan
• What Is a Cut List in Woodworking? (And How to Use One)
• Woodworking Measurements Guide: Imperial, Metric & Lumber Sizes
• The Complete Beginner’s Guide to Woodworking Plans