Inches to MM Converter
Quick answer
1 inch (in) = 25.4 millimetres (mm) exactly, so multiply inches by 25.4 for millimetres and divide millimetres by 25.4 for inches. 12 in = 304.8 mm, 24 in = 609.6 mm, and 1 mm = 0.03937 in.
How to measure before converting inches to millimetres
The Inches to MM Converter turns imperial inch measurements into metric millimetres, centimetres (cm), and metres (m) with the exact SI factor of 25.4 mm per inch defined by the 1959 international yard and pound agreement. Decimal inches (3.5"), fractional inches (3 1/2", 1/4", 5/8"), feet-and-inch readings (4 ft 2 in), and millimetre inputs from a metric tape measure, digital caliper, steel ruler, or laser distance meter convert through that single constant.
Record three measurements for a panel, sheet, box, tile, or plywood cut: length across the longest horizontal edge, width through the front-to-back depth, and height from bottom to top. Keep the tape square to the edge, read the nearest 1/16 inch (1.5875 mm) mark, and enter each figure in the matching Length, Width, or Height field for machine-ready dimensions such as 1219.2 × 609.6 × 152.4 mm.
- 1Enter the inch valueType 12, 3.5, or 3 1/2 in the single-value field, or fill Length, Width, and Height for full L × W × H dimensions.
- 2Pick the roundingSelect 0–4 decimal places for workshop tolerances, engineering drawings, or CNC cut lists.
- 3Read every unitCollect millimetres, centimetres, metres, feet-plus-inches, area in square feet (sq ft) and square metres (sq m), plus volume in cubic feet (cu ft).
Inches to MM Converter
Length = longest horizontal side (left → right). Width = depth (front → back). Height = vertical side (bottom → top).
Estimated cost (optional)
Enter a material rate to estimate a budget from your converted size.
Reference only: rate × billable area/length, plus waste. Typical market rates run about $2–$45 per sq ft for tile and flooring materials, and roughly $10–$60 per sq yd for carpet — multiply a sq ft rate by 9 for sq yd, or by 10.764 for sq m.
Which side is which
Quick reference
| Inches | Millimetres | Centimetres |
|---|
1 in = 25.4 mm exactly · 1 mm = 0.03937 in
How the Inches to MM Converter works
The Inches to MM Converter multiplies every inch value by the exact factor 25.4 and prints the millimetre result instantly, with no page reload, because the calculation runs in the browser as each keystroke, preset chip, or dropdown change fires. Single-value mode handles decimal inches (7.25"), fractional inches (5/8"), and reverse millimetre input, while L × W × H mode converts three edges at once and derives area in square feet (sq ft), square yards (sq yd), square metres (sq m), plus volume in cubic feet (cu ft). The optional cost estimator multiplies the converted area or linear length by your material rate, quantity, and waste percentage to return a budget figure in US dollars ($).
Inches to MM formula
Inches to MM Converter examples
Single-value conversions
A 12-inch measurement equals 304.8 mm, 30.48 cm, 0.3048 m, and 1 ft 0 in. Four common shop values convert as shown.
Full L × W × H example
A 48 × 24 × 6 inch panel converts to 1219.2 × 609.6 × 152.4 mm, covering 8 sq ft (0.743 sq m, 0.889 sq yd) with a volume of 4 cu ft (0.113 cu m). Length runs 48 in left to right, width runs 24 in front to back, and height rises 6 in from bottom to top.
| Measurement | Inches (in) | Millimetres (mm) | Centimetres (cm) | Metres (m) |
|---|---|---|---|---|
| Length (L) | 48 in | 1,219.2 mm | 121.92 cm | 1.2192 m |
| Width (W) | 24 in | 609.6 mm | 60.96 cm | 0.6096 m |
| Height (H) | 6 in | 152.4 mm | 15.24 cm | 0.1524 m |
| Face diagonal | 53.67 in | 1,363.1 mm | 136.31 cm | 1.3631 m |
| Face perimeter | 144 in | 3,657.6 mm | 365.76 cm | 3.6576 m |
Estimated cost example
An 8 sq ft panel priced at $8.00 per sq ft with 1 piece and 10% waste costs $70.40. Four rate units return the same total for one 48 × 24 in surface.
| Rate unit | Billable quantity | Rate | Total with 10% waste |
|---|---|---|---|
| Per square foot | 8.00 sq ft | $8.00 | $70.40 |
| Per square yard | 0.89 sq yd | $72.00 | $70.40 |
| Per square metre | 0.743 sq m | $86.11 | $70.40 |
| Per linear foot | 4.00 linear ft | $16.00 | $70.40 |
Helpful information before you convert inches to millimetres
Measure twice, convert once, and keep 2 decimal places for construction work or 4 decimal places for machining. The inch (in), millimetre (mm), centimetre (cm), and metre (m) sit on one fixed chain of exact factors, so conversion accuracy depends on measurement quality rather than the arithmetic.
5 checks to run before entering a value
- Confirm the unit on the tape: imperial tapes mark 1/8 and 1/16 inch, metric tapes mark 1 mm and 0.5 cm.
- Zero the caliper: digital calipers drift, and a 0.02 in offset shifts the result by 0.508 mm.
- Convert fractions correctly: 1/16 in = 1.5875 mm, 1/8 in = 3.175 mm, 3/4 in = 19.05 mm.
- Separate nominal from actual sizes: nominal 2×4 lumber measures 1.5 × 3.5 in (38.1 × 88.9 mm), and nominal 1/2 in drywall measures 0.5 in (12.7 mm).
- Choose the rounding last: round the final millimetre figure, never the intermediate inch value.
Where millimetre precision matters
- CNC and 3D printing: G-code, CAD drawings, and slicer settings accept millimetres, with tolerances of ±0.1 mm.
- Cabinet and furniture builds: European hardware uses 32 mm system spacing and 8 mm dowel holes.
- Screen and print sizes: a 6.1 in phone display spans 154.94 mm diagonally, and A4 paper measures 210 × 297 mm (8.27 × 11.69 in).
- Plumbing and fasteners: a 1/2 in pipe thread pairs with 12.7 mm stock, and an M8 bolt spans 8 mm (0.315 in).
- Tile and flooring layouts: a 12 × 24 in tile equals 304.8 × 609.6 mm, with 3 mm (0.118 in) grout joints.
Cost estimate accuracy
Tile and flooring materials sell for roughly $2–$45 per sq ft, carpet sells for $10–$60 per sq yd, and installed flooring projects run $4–$28 per sq ft. Multiply a sq ft rate by 9 for a sq yd rate, or by 10.764 for a sq m rate, then add 10% waste for straight cuts and 15% for diagonal or herringbone layouts.
Rounding rules that protect a cut list
Keep 1 decimal place for framing (0.1 mm), 2 decimal places for joinery (0.01 mm), and 3–4 decimal places for tooling. A 0.5 mm error repeated across 8 panels compounds to 4 mm, enough to close a cabinet gap incorrectly.
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Frequently asked questions (FAQs)
1How many millimetres are in 1 inch?
1 inch contains 25.4 millimetres exactly. The value is a definition, so 2 in = 50.8 mm, 10 in = 254 mm, and 100 in = 2,540 mm carry zero rounding error.
2How do I convert inches to mm manually?
Multiply the inch value by 25.4. A 7.5 in board becomes 7.5 × 25.4 = 190.5 mm, and a 5/8 in gap becomes 0.625 × 25.4 = 15.875 mm.
3Does the Inches to MM Converter accept fractions?
Yes, fractional and mixed inch entries convert directly. Type 1/4, 5/8, 3 1/2, or 15 3/16, and the converter resolves each fraction to a decimal before applying the 25.4 factor.
4Which side is length, width, and height?
Length runs side to side along the longest horizontal edge, width runs front to back as depth, and height runs bottom to top vertically. Shipping labels and cut lists follow the same L × W × H order, such as 48 × 24 × 6 in.
5Is 25.4 mm per inch the same in every country?
Yes, the international inch equals 25.4 mm worldwide. The 1959 international yard and pound agreement between the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa fixed the factor, and the US survey inch of 25.4000508 mm was retired on 31 December 2022.
6How many decimal places should I keep?
Keep 1–2 decimal places for construction and 3–4 decimal places for machining. Framing tolerates 0.5 mm, cabinetry tolerates 0.1 mm, and CNC milling tolerates 0.01 mm.
7How does the cost estimate work?
The cost estimate multiplies your material rate by the converted area or linear length, then applies quantity and waste percentage. Rates accept $ per sq ft, sq yd, sq m, linear ft, linear m, or piece, and a 48 × 24 in panel at $8 per sq ft with 10% waste returns $70.40.
8Can the converter run the reverse mm to inches direction?
Yes, the swap direction button converts millimetres to inches. Entering 304.8 mm returns 12 in, 1,000 mm returns 39.37 in (3 ft 3.37 in), and 25 mm returns 0.98 in.
9What are the most searched inch to mm values?
1 in = 25.4 mm, 2 in = 50.8 mm, 4 in = 101.6 mm, 6 in = 152.4 mm, 12 in = 304.8 mm, and 24 in = 609.6 mm rank as the 6 most requested conversions. Fractional favourites include 1/8 in = 3.175 mm, 1/4 in = 6.35 mm, and 3/4 in = 19.05 mm.