Key Conversion Factors
1 foot = 304.8 mm = 30.48 cm = 0.3048 m = 12 in
1 yard = 914.4 mm = 91.44 cm = 0.9144 m = 36 in = 3 ft
1 mm = 0.03937 in = 0.003281 ft
1 m = 1000 mm = 39.370 in = 3.2808 ft = 1.0936 yd
Standard Round Duct Sizes -- Imperial to Metric
| Nominal (in) | Actual OD (mm) | Typical Use |
|---|---|---|
| 4 in | 102 mm | Small branch, bathroom exhaust |
| 5 in | 127 mm | Bedroom supply branch |
| 6 in | 152 mm | Most common residential branch |
| 7 in | 178 mm | Larger bedroom / zone branch |
| 8 in | 203 mm | Main branch or large room supply |
| 9 in | 229 mm | Sub-main duct run |
| 10 in | 254 mm | Main trunk branch |
| 12 in | 305 mm | Main trunk or large branch |
| 14 in | 356 mm | Commercial main trunk |
| 16 in | 406 mm | Large commercial main trunk |
| 18 in | 457 mm | Commercial main or plenum |
| 20 in | 508 mm | Large commercial main |
| 24 in | 610 mm | Industrial / large commercial |
ACR Copper Tubing Sizes -- Refrigerant Piping
| ACR Size (OD in) | OD (mm) | Wall (mm) | Typical Application |
|---|---|---|---|
| 1/4 in (0.250) | 6.35 | 0.76 | Capillary, small appliances |
| 3/8 in (0.375) | 9.53 | 0.89 | Mini-split liquid line |
| 1/2 in (0.500) | 12.70 | 0.89 | Mini-split suction, small AC liquid |
| 5/8 in (0.625) | 15.88 | 1.02 | Common split AC suction line |
| 3/4 in (0.750) | 19.05 | 1.07 | Larger split AC suction |
| 7/8 in (0.875) | 22.23 | 1.14 | 3-5 ton AC suction line |
| 1-1/8 in (1.125) | 28.58 | 1.27 | Larger commercial suction |
| 1-3/8 in (1.375) | 34.93 | 1.40 | Commercial refrigeration suction |
| 1-5/8 in (1.625) | 41.28 | 1.52 | Large commercial suction |
ACR copper tubing is sized by actual outside diameter -- not nominal pipe size. Per SOR/2016-137 and CSA B52, only ACR-grade copper (not plumbing copper) is approved for refrigerant piping in Canada. Always verify tubing specification before installation.
Common HVAC Installation Clearances
| Clearance / Dimension | Imperial | Metric | Reference |
|---|---|---|---|
| Furnace front service clearance | 24 in min. | 610 mm | Manufacturer / NBC |
| Furnace side clearance (combustible) | 1 in min. | 25 mm | Manufacturer requirement |
| Gas appliance flue clearance | 6 in min. | 152 mm | NBC / CGA B149.1 |
| Condenser unit clearance (sides) | 12-18 in | 305-457 mm | Manufacturer specification |
| Condenser unit clearance (top) | 60 in min. | 1524 mm | Unrestricted discharge required |
| Supply diffuser to thermostat | 5 ft min. | 1524 mm | ASHRAE 55 comfort guidance |
| Return air grille clearance | 6 in from corner | 152 mm | Avoid dead zones |
| Refrigerant line set clearance | 6 in from flue | 152 mm | CSA B52 isolation requirement |
| Ceiling height (minimum residential) | 7 ft 6 in | 2286 mm | NBC Part 9 |
| Mechanical room height (minimum) | 7 ft | 2134 mm | NBC / typical AHJ requirement |
How to Use the Length Converter
Enter a value in mm, cm, m, inches, feet, or yards. All other units update instantly. Use the quick-reference presets for common HVAC dimensions: ceiling heights, round duct diameters, and standard duct run lengths.
The result panel identifies what HVAC dimension category your length falls in: pipe or tubing diameter, duct size, room dimension, equipment clearance, or large-scale duct run. This helps verify a converted value matches the expected scale for the application.
Three reference tables cover standard round duct sizes (Imperial to metric), ACR copper tubing outside diameters for refrigerant piping, and common HVAC installation clearances. Use these alongside Canadian code references to verify converted dimensions against actual equipment and code requirements.
Converted duct dimensions feed into the Duct Sizing Calculator. Room dimensions in metres feed into the Heat Load Calculator and Area Converter. Pipe dimensions support refrigerant line sizing in the Refrigeration tools.
Length Units in HVAC -- Complete Guide
Canadian HVAC work spans two measurement systems daily. Equipment dimensions, pipe diameters, duct sizes, and fitting specs arrive in Imperial from US manufacturers. Building drawings, engineering specifications, and permits use metric. Converting fluently between mm, cm, m, inches, and feet prevents installation errors and drawing coordination problems.
Inches to Millimetres -- The Daily Conversion
The fundamental relationship is exact: 1 inch = 25.4 mm. This means 6 inches = 152.4 mm, 12 inches = 304.8 mm, and 1 foot = 304.8 mm. For HVAC field work, memorizing the key multiples is faster than reaching for a converter: 4 in = 102 mm, 6 in = 152 mm, 8 in = 203 mm, 10 in = 254 mm, 12 in = 305 mm. Duct sizing, pipe stub-out locations, and equipment footprints all benefit from these quick conversions. For area conversions of duct cross-sections, use the Area Converter.
Feet to Metres for Room and Building Dimensions
Room dimensions in Canada are documented in metres on architectural drawings but are still frequently discussed in feet and inches in the field. The conversion: 1 foot = 0.3048 m, so 1 m = 3.2808 ft. Common residential ceiling heights: 8 ft = 2.438 m, 9 ft = 2.743 m, 10 ft = 3.048 m. Standard stud-frame wall height: 9 ft = 2.743 m (common in new construction). A 20 x 15 ft room is 6.096 x 4.572 m with a floor area of 27.87 m². Feed room dimensions in metres into the Heat Load Calculator for accurate load analysis.
ACR Copper Tubing for Refrigerant Piping
Refrigerant line sets in Canada use ACR (Air Conditioning and Refrigeration) copper tubing, which is specified by actual outside diameter in inches. This differs from plumbing copper, which uses nominal sizes. A 3/4-inch ACR tube has an actual OD of 0.750 inches (19.05 mm). Canadian regulations under SOR/2016-137 and CSA B52 (Mechanical Refrigeration Code) require ACR-grade copper -- not plumbing-grade copper -- for all refrigerant piping. When working from Canadian drawings that specify metric, convert the millimetre OD back to inches to identify the correct ACR tube size from a supplier catalogue.
Duct Dimensions and Coordination
Round duct in Canada is specified in inches by HVAC contractors but appears in mm on structural and architectural drawings. A 10-inch round duct needs 254 mm of clear space plus insulation -- typically adding 50-75 mm on each side. Rectangular duct dimensions in Imperial (e.g., 16x10) convert directly: 16 in = 406 mm, 10 in = 254 mm. BIM coordination between HVAC, structural, and electrical trades requires all dimensions in the same unit -- typically mm for Canadian projects. The Duct Sizing Calculator works in both units and shows equivalent sizes for coordination.
Installation Clearances and Code Compliance
The National Building Code of Canada and equipment manufacturer requirements specify minimum clearances. These appear in both Imperial and metric depending on whether the source is a Canadian code (metric) or a US manufacturer (Imperial). A furnace requiring 24-inch front service clearance needs 610 mm of unobstructed space. An outdoor condenser requiring 60 inches of overhead clearance needs 1524 mm. Always check the clearance table above when interpreting installation documents that mix unit systems -- a clearance misread as inches instead of mm would leave equipment inaccessible for service.
Frequently Asked Questions
Multiply inches by 25.4 to get millimetres. So 1 in = 25.4 mm, 6 in = 152.4 mm, and 12 in = 304.8 mm. To go the other way, divide mm by 25.4. Key HVAC multiples to memorize: 4 in = 102 mm, 6 in = 152 mm, 8 in = 203 mm, 10 in = 254 mm, 12 in = 305 mm. These cover the most common round duct branch sizes used in Canadian residential work.
Multiply feet by 0.3048 to get metres. To go the other way, multiply metres by 3.2808. Common HVAC reference points: 8 ft ceiling = 2.438 m, 9 ft ceiling = 2.743 m, 10 ft mechanical room = 3.048 m. For quick field estimates, 3 ft is close to 1 m (actually 0.914 m), and 10 ft is close to 3 m (actually 3.048 m). For room areas using converted dimensions, use the Area Converter.
Rectangular duct follows SMACNA standard sizes specified in inches. Common residential sizes: 8x6 (203x152 mm), 10x6 (254x152 mm), 12x8 (305x203 mm), 14x8 (356x203 mm). Common commercial sizes: 16x10 (406x254 mm), 18x12 (457x305 mm), 24x14 (610x356 mm). Canadian duct suppliers stock these standard sizes and fittings in both Imperial-labelled and metric-labelled catalogues. Always confirm with your local supplier which labelling system applies to the fittings you're ordering.
Nominal pipe size (NPS) does not equal actual outside diameter for smaller sizes. A 1-inch NPS copper pipe has an actual OD of 1.125 inches (28.6 mm). ACR copper for refrigerant piping is different -- it's sized by actual OD directly: 3/4-inch ACR tube is exactly 0.750 inches (19.05 mm) OD. When converting between Canadian metric drawings and US-sourced ACR tubing catalogues, always use the actual OD in mm from the table above rather than the nominal pipe size to avoid ordering the wrong tube size.