What is the easiest way to convert millimeters to inches for DIY?

Divide by 25.4 to get inches exactly. For rough mental math, divide by 25 (1 mm equals about 0.04 inches, so 100 mm equals about 4 inches). Most home-store calculators have a direct mm-to-inch button, and many tape measures have both scales on opposite sides of the blade.

Are IKEA dimensions in millimeters or centimeters?

IKEA publishes dimensions in centimeters on packaging and assembly instructions for most furniture, with a millimeter precision on technical drawings for cabinetry and built-ins. The IKEA US website also shows inches alongside centimeters, but the assembly steps use only centimeters.

How accurate do I need to be when converting metric to imperial for woodworking?

For furniture-grade work, round to the nearest 1/16 inch (which is about 1.6 mm). For framing carpentry, round to the nearest 1/8 inch (3.2 mm). For tile work or trim, round to the nearest 1/32 inch (0.8 mm) and recheck after each cut. The metric-imperial conversion error compounds across joints, so always reconvert from the original metric value rather than chaining inch-to-inch additions.

What if my European appliance dimensions don't fit American cabinets?

European appliances often differ from American by 25 to 50 mm (1 to 2 inches). A 600 mm European dishwasher is 23.6 in, slightly narrower than a US 24 in slot. Always measure the actual cabinet opening in millimeters before ordering, and confirm depth, width, and height separately. The width is usually the most reliable spec, depth varies most.

Can I just print the European plans and use a metric tape?

Yes, and many DIYers prefer that. A 5-meter metric tape costs the same as an imperial tape and is available at any hardware store. For complex projects with both metric and imperial materials, using metric tools throughout reduces conversion errors and matches the original design.

How to Convert Metric Blueprints to Feet and Inches for DIY Projects

The short answer

The cleanest approach is to measure once in millimeters and convert in batches. Lay out the entire metric plan, convert all key dimensions to inches at the precision you need (typically 1/16 in for furniture, 1/8 in for framing), then double-check by reconverting the inches back to millimeters to catch rounding drift.

For most DIY projects, the conversion factor that matters is 1 mm = 0.0394 in (or equivalently, 1 in = 25.4 mm exactly). The 1 foot = 0.3048 m relationship is fixed by the 1959 International Yard and Pound Agreement, so the math always lines up to clean values if you start from the millimeter side.

This guide walks through a practical workflow for converting metric architectural and assembly plans into something you can cut with an American framing square and a 25-foot imperial tape.

The two unit systems you’ll see

European, Asian, and Australian/New Zealand plans use the metric system, but they pick different units depending on context:

Architectural plans: millimeters or centimeters. A floor plan dimension like “3500” means 3500 mm (3.5 m) unless the units are explicitly noted as cm. Always check the legend.
IKEA assembly: centimeters on packaging, millimeters on detailed drawings for built-in cabinetry (PAX, METOD).
Kitchen appliance specs: millimeters for width/depth/height, sometimes in 600/900 mm “Euro” modular sizes.
Tile and stone work: millimeters for thickness, centimeters for tile dimensions, square meters for area pricing.
Lumber sizes (Europe): millimeters. A “70x140” board is 70 mm × 140 mm cross-section.

American plans use a mix of feet, inches, and fractions:

Architectural: feet and inches, often as feet-and-inches notation like “3’-6 1/2"" (3 feet 6.5 inches).
Framing carpentry: nominal lumber sizes in inches (a “2x4” is actually 1.5 in × 3.5 in milled).
Cabinetry: inches with 1/16 in or 1/32 in precision.

The conversion is mechanical, but the unit conventions are not. If you import a German kitchen design and a US framer is building the rough opening, you need to make sure both sides agree on what dimension is being given.

The reference values worth memorizing

For converting between mm and inches in your head, memorize:

mm	inches	Common use
10 mm	0.39 in	metric centimeter
25.4 mm	1.00 in	the canonical conversion anchor
50 mm	1.97 in	roughly 2 in (off by 1/32)
100 mm	3.94 in	roughly 4 in (off by 1/16)
150 mm	5.91 in	roughly 6 in (off by 3/32)
200 mm	7.87 in	roughly 8 in (off by 1/8)
250 mm	9.84 in	roughly 10 in (off by 5/32)
300 mm	11.81 in	roughly 12 in / 1 ft (off by 3/16)
304.8 mm	12.00 in	exactly 1 ft (the 1959 conversion)
600 mm	23.62 in	Euro standard cabinet width
800 mm	31.50 in	wide Euro cabinet
1000 mm	39.37 in	1 metre
1830 mm	72.05 in	1.83 m, 6 ft door height
2400 mm	94.49 in	2.4 m ceiling height
2438 mm	96.00 in	exactly 8 ft (sheet goods height)
3050 mm	120.08 in	10 ft

Note that the metric “round” sizes (300, 600, 1000) do not align with imperial round sizes (12 in, 24 in, 36 in). A 600 mm cabinet is not 24 inches, it is 23.6 inches. For DIY work, this 0.4 in difference is enough to matter when fitting into a stud bay or an existing opening.

The workflow

Step 1: get the original plan in its native units. If it is a PDF from a European architect, do not let any intermediate tool re-render the dimensions. Some conversion services round to two decimal places (cm to in) which loses 0.4 mm of precision per dimension.

Step 2: identify the critical dimensions. These are the ones that interface with US-supplied materials (drywall, lumber, appliances). Mark them on the plan. For a kitchen install, that is the cabinet face widths, the appliance opening widths, the ceiling height, and the floor-to-counter height.

Step 3: convert critical dimensions to inches using the exact factor (divide mm by 25.4). Use a meters-to-feet calculator for sanity-checks on larger dimensions. Round to the precision you need:

1/32 in for trim work and joinery (about 0.8 mm)
1/16 in for furniture and cabinetry (about 1.6 mm)
1/8 in for framing and rough carpentry (about 3.2 mm)

Step 4: write the converted dimensions back onto the plan in feet-and-inches notation. Keep the original metric dimension visible too, so you can refer back without redoing the conversion.

Step 5: order US materials at the rounded inch value. For example, a European 2440 mm ceiling becomes a 96 in ceiling (8 ft exactly, the standard US drywall sheet). The 2 mm gap (2440 mm vs 2438.4 mm for 96 in) is invisible to a framer.

Step 6: cut and fit. If a tolerance gap appears, it should be at a finish-trim joint where caulk or a reveal can hide it, not at a structural or load-bearing connection.

IKEA-specific tips

IKEA is the most common case where US DIYers run into metric dimensions. Their published cabinet sizes are in millimeters and follow a system:

METOD kitchen cabinets: 200, 400, 600, 800, 1000, 1200 mm widths. The 600 mm (24 in nominal) is the workhorse.
PAX wardrobes: 500, 750, 1000 mm widths. The 1000 mm (39 in) is wider than US standard closet rod hardware.
BESTÅ TV storage: 600, 1200, 1800 mm widths with 200, 400 mm depths.

For an IKEA install in an American home, the safest approach is:

Measure the wall opening in millimeters using a metric tape (cheap, available at Home Depot or Lowe’s).
Pick IKEA components that sum to slightly less than the opening (10 to 20 mm gap).
Fill the gap with the IKEA filler pieces, which come in 100, 200, 400 mm widths and are designed for trimming on site.

The mistake to avoid is measuring the wall in inches and trying to convert to mm to select IKEA components. The conversion error from the rounded inch reading propagates through. Always measure in the native unit of the components you plan to install.

Tools that help

A few specific tools save time on metric-to-imperial DIY work:

Dual-scale tape measure. Both Stanley and Komelon sell tapes with millimeters on the top edge and inches on the bottom. The 25-foot version is the right length for residential work. Cost: $15-25.
Construction calculator (Calculated Industries Construction Master Pro, app or hardware). It handles feet-inch-fraction math natively and has a metric conversion button. The cheap Android app version works fine for most use.
A reference card taped to the wall of your workshop with the conversion values from the table above. Sounds obvious but having it stuck to the wall removes one cognitive step per conversion.
Imperial-metric drill bit set. If the original plan calls for 8 mm bolts in a 9 mm pilot hole, having a metric drill bit set is faster than converting to the nearest imperial fraction. Available at any auto parts store as well as hardware stores.

The cost of going fully metric for one project is about $40 of tools. For anyone who does more than one IKEA install or imports one European appliance, that is a one-time investment that pays back on the second project.

Mistakes to avoid

The two most common errors:

Chained conversions. Converting mm to inches, then inches to fractional inches, then adding the fractions together accumulates rounding error. Always sum the original mm values first, then convert the total to inches once.

Confusing 1 m and 1 ft. They differ by 33 cm (about 13 in), which is enough to be a real problem on a plan but small enough to slip past inattentive reading. If a plan dimension looks weirdly out of scale, the most likely cause is a mis-read of the unit, not a measurement error.

For more on the mental math of meter-to-foot conversion, our guide on mental math conversion tricks covers the techniques that work reliably without a calculator.

Sources and further reading: