Divide the millimetres by 304.8
One foot is exactly 304.8 mm, because the inch is defined as exactly 25.4 mm and a foot is twelve of them. For a rough figure in your head, divide by 300 instead of 304.8 — that treats a foot as 300 mm and lands within about 2%.
Quick reference
| Millimetres | Feet | Feet & inches |
|---|---|---|
| 100 mm | 0.33 ft | 3.94 in |
| 152.4 mm | 0.50 ft | 6 in |
| 304.8 mm | 1.00 ft | 1 ft 0 in |
| 609.6 mm | 2.00 ft | 2 ft 0 in |
| 1,000 mm | 3.28 ft | 3 ft 3.4 in |
| 1,524 mm | 5.00 ft | 5 ft 0 in |
| 3,048 mm | 10.0 ft | 10 ft 0 in |
Whole-foot values land on exact millimetres (304.8, 609.6, 914.4…), which is why round metric numbers like 1,000 mm never come out to a tidy figure in feet.
Decimal feet vs feet and inches
- Two ways to write it. 3.28 ft and 3 ft 3.4 in are the same length. The fractional part of the decimal is the inches: 0.28 ft × 12 = 3.4 in.
- Old US survey foot. Modern conversions use the international foot (0.3048 m exactly). Pre-1959 US survey feet differ by a hair — it only matters in land surveying, not construction.
Common questions
How do I convert millimetres to feet?
Divide the millimetres by 304.8. So 1,000 mm is 1,000 divided by 304.8, which is 3.28 feet. To go the other way, multiply feet by 304.8.
Why is one foot exactly 304.8 mm?
Since 1959 the inch has been defined as exactly 25.4 mm. A foot is 12 inches, so 12 times 25.4 gives 304.8 mm exactly. It is a definition, not a rounded figure.
Is there a quick mental estimate?
Treat one foot as about 300 mm and divide by 300. For 600 mm that gives roughly 2 feet; the exact answer is 1.97 feet, so the estimate is close enough for a rough check.
