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Length Converter: mm, cm, m, km, inch, foot, yard and mile
Base unit: meter (m)1 in = 25.4 mm (exact)
Use the length converter to switch between metric units (mm, cm, m, km) and imperial units (inch, foot, yard, mile) on drawings, datasheets and site measurements. The underlying unit definitions are exact, so repeated conversions do not drift; values shown with ≈ are rounded for readability.
Exact length conversion factors
| Unit | In meters | Definition |
|---|
| 1 inch (in) | 0.0254 m | Exactly 25.4 mm |
| 1 foot (ft) | 0.3048 m | 12 inches |
| 1 yard (yd) | 0.9144 m | 3 feet |
| 1 mile (mi) | 1,609.344 m | 5,280 feet |
| 1 meter (m) | 1 m | ≈ 3.28084 ft |
How to convert length
Multiply by the factor of the unit you have, then divide by the factor of the unit you want. Example: 12 in × 25.4 = 304.8 mm, and 100 m ÷ 0.3048 = 328.084 ft.
Where length conversion is used
- Drawings and fabrication: checking metric drawing dimensions against inch callouts on imported machinery, fasteners and pipe fittings.
- Cable and conduit takeoffs: reconciling run lengths quoted in meters and feet in the same bill of quantities.
- Route and site surveys: converting miles to kilometers for transmission line, pipeline or road distances.
- Tolerances: reading thousandths of an inch (mils) correctly against a metric micrometer.
Mistakes to avoid
- Wrong direction: multiplying when you should divide gives an inverted result. The factor line under the result always shows “1 unit = X unit”.
- Using length factors for area: area factors are squared, so use the Area converter instead of applying 0.3048 to ft².
Area Converter: mm², cm², m², km², in², ft², acre and hectare
Base unit: square meter (m²)1 ft² = 0.09290304 m²
The area converter handles metric areas, imperial areas and land units such as the acre and hectare. Area factors are the square of length factors, so they are stored ready-squared to avoid the most common manual error.
Exact area conversion factors
| Unit | In square meters | Useful equivalent |
|---|
| 1 in² | 0.00064516 m² | 645.16 mm² |
| 1 ft² | 0.09290304 m² | 144 in² |
| 1 acre | 4,046.8564224 m² | 43,560 ft² |
| 1 hectare (ha) | 10,000 m² | ≈ 2.47105 acres |
| 1 m² | 1 m² | ≈ 10.7639 ft² |
How to convert area
Multiply by the square-meter factor of the starting unit and divide by the factor of the target unit. Example: a 5,000 ft² roof × 0.09290304 = 464.515 m².
Where area conversion is used
- Land and site planning: moving between acres or hectares in land records and m² or ft² in layouts.
- Solar projects: checking usable roof or ground area against panel counts and array layouts.
- Sheet metal and insulation: comparing ft² quantities on imported datasheets with metric fabrication drawings.
- Conductor cross-sections: keeping cable and busbar areas consistently in mm².
Mistakes to avoid
- Applying a length factor: 1 m = 3.28 ft, but 1 m² = 10.76 ft², not 3.28 ft².
- Mixing acre and hectare: a hectare is about 2.47 times larger than an acre, a large error over a whole site.
Weight Converter: mg, g, kg, metric ton, pound and ounce
Base unit: kilogram (kg)1 lb = 0.45359237 kg (exact)
The weight (mass) converter moves between the metric scale (mg, g, kg, metric ton) and pounds and ounces. It uses the exact international pound instead of the rounded 2.2 lb/kg rule of thumb.
Exact weight conversion factors
| Unit | In kilograms | Useful equivalent |
|---|
| 1 ounce (oz) | 0.028349523125 kg | ≈ 28.3495 g |
| 1 pound (lb) | 0.45359237 kg | 16 oz |
| 1 metric ton (t) | 1,000 kg | ≈ 2,204.62 lb |
| 1 short ton (US) | 907.18474 kg | 2,000 lb (not in converter) |
| 1 long ton (UK) | 1,016.0469 kg | 2,240 lb (not in converter) |
How to convert weight
Multiply by the kilogram factor of the starting unit and divide by the target unit's factor. Example: a 550 lb motor × 0.45359237 = 249.476 kg.
Where weight conversion is used
- Lifting plans: checking nameplate weights in lb against crane or forklift capacity in kg or tonnes.
- Procurement and freight: comparing supplier prices per ounce or pound with metric bills of materials.
- Structural loads: adding battery, panel or equipment weights to roof or floor load checks.
- Foundations: using total transformer or skid weight for plinth and foundation design.
Mistakes to avoid
- Ambiguous “ton”: confirm whether a document means a metric ton, US short ton or UK long ton before relying on the figure.
- Rounded 2.2 factor: fine for a quick estimate, but the error adds up across long material lists.
Pressure Converter: Pa, kPa, bar, psi, atm, mmHg and kgf/cm²
Base unit: pascal (Pa)1 bar = 14.5038 psi
The pressure converter covers SI units (Pa, kPa), bar, psi, standard atmospheres, mmHg and the gravitational kgf/cm² still printed on many gauges. All values are converted through the pascal.
Pressure conversion factors
| Unit | In pascals | In psi |
|---|
| 1 bar | 100,000 Pa | ≈ 14.5038 psi |
| 1 psi | 6,894.757 Pa | 1 psi |
| 1 atm | 101,325 Pa | ≈ 14.6959 psi |
| 1 kgf/cm² | 98,066.5 Pa | ≈ 14.2233 psi |
| 1 mmHg | 133.322 Pa | ≈ 0.019337 psi |
How to convert pressure
Multiply by the pascal factor of the starting unit and divide by the target factor. Example: 150 psi × 6,894.757 ÷ 100,000 = 10.342 bar.
Where pressure conversion is used
- Compressed air and hydraulics: matching psi-rated cylinders and valves to a system set in bar.
- Boilers and vessels: comparing gauge readings in kgf/cm² with design pressures in kPa or bar.
- Vacuum and pumps: turning mmHg suction figures into kPa or bar.
- Altitude derating: expressing site barometric pressure in the same unit as a compressor or genset derating chart.
Mistakes to avoid
- Gauge vs absolute: this tool converts pressure units; it does not convert gauge pressure to absolute pressure. For example, at approximately atmospheric pressure, 1 barg ≈ 2.013 bara, so keep the same basis on both sides.
- Safety-critical values: for relief valve set points and pressure vessel documents, confirm the final value against the applicable code.
Temperature Converter: Celsius, Fahrenheit and Kelvin
°F = °C × 9/5 + 32K = °C + 273.15
Temperature conversion uses offset formulas, not a single factor, because Celsius, Fahrenheit and Kelvin start from different zero points. The converter goes through Celsius internally and applies the full formula in both directions.
Temperature conversion formulas
| From → To | Formula | Example |
|---|
| °C → °F | °F = °C × 9/5 + 32 | 40 °C = 104 °F |
| °F → °C | °C = (°F − 32) × 5/9 | 212 °F = 100 °C |
| °C → K | K = °C + 273.15 | 25 °C = 298.15 K |
| K → °C | °C = K − 273.15 | 0 K = −273.15 °C |
| Absolute zero | 0 K | −459.67 °F |
Temperature values vs temperature differences
A reading needs the full formula, but a change in temperature only uses the scale factor: a rise of 10 °C (10 K) equals a rise of 18 °F, not 50 °F. Use this converter for readings, and multiply differences by 1.8 (°C to °F) yourself.
Where temperature conversion is used
- Motors and insulation: comparing °F limits on imported datasheets with °C insulation classes under IEC 60034.
- HVAC and chillers: moving setpoints between °F equipment and a °C building management system.
- Cable derating: keeping ambient and conductor temperatures in °C before applying derating factors.
- Science and lighting: Kelvin for thermodynamic formulas and LED color temperature.
Mistakes to avoid
- Treating it like a ratio: doubling °C does not double °F.
- Converting a rise with the offset: adding 32 to a temperature difference gives a badly wrong result.
Energy Converter: J, kJ, cal, kcal, Wh, kWh and BTU
Base unit: joule (J)1 kWh = 3,600 kJ
The energy converter links SI units (J, kJ), electrical units (Wh, kWh), food and heat units (cal, kcal) and the BTU used on many HVAC ratings. All units are pure multiples of the joule.
Energy conversion factors
| Unit | In joules | Useful equivalent |
|---|
| 1 calorie (cal) | 4.184 J | Thermochemical calorie |
| 1 kilocalorie (kcal) | 4,184 J | 1,000 cal |
| 1 watt-hour (Wh) | 3,600 J | 1 W for 1 hour |
| 1 kilowatt-hour (kWh) | 3,600,000 J | ≈ 3,412.14 BTU |
| 1 BTU | 1,055.056 J | International Table BTU |
How to convert energy
Multiply by the joule factor of the starting unit and divide by the target factor. Example: 12,000 BTU = 3.517 kWh of energy. As a rate, 12,000 BTU/h corresponds to about 3.517 kW of cooling capacity.
Where energy conversion is used
- Electricity and solar: daily yield, bills and load profiles in kWh.
- Batteries and UPS: Ah × V gives Wh, which can then be compared with load energy in kWh.
- HVAC: comparing BTU cooling ratings with kW-based heat loads.
- Thermal calculations: converting kcal or BTU data into kJ for process heat balances.
Mistakes to avoid
- Cooling vs electrical input: 3.517 kW of cooling is not 3.517 kW of electricity; input power depends on the unit's EER or COP.
- Calorie variants: this tool uses the 4.184 J thermochemical calorie. The International Table calorie is 4.1868 J, a 0.07% difference.
Flow Rate Converter: m³/s, m³/h, L/s, L/min, US GPM and CFM
Base unit: m³/s1 US GPM = 3.78541 L/min
The flow rate converter handles volumetric flow for pumps, piping, water treatment and HVAC airflow. It uses the US liquid gallon for GPM. CFM is treated as a volumetric flow unit based on the cubic-foot volume definition; standard or actual gas-flow conditions such as SCFM are not converted.
Flow rate conversion factors
| Unit | In m³/h | Useful equivalent |
|---|
| 1 L/s | 3.6 m³/h | 60 L/min |
| 1 L/min | 0.06 m³/h | ≈ 0.26417 US GPM |
| 1 US GPM | 0.227125 m³/h | 3.785411784 L/min |
| 1 CFM | 1.699011 m³/h | 28.316847 L/min |
| 1 m³/h | 1 m³/h | ≈ 0.58858 CFM |
How to convert flow rate
Multiply by the m³/s factor of the starting unit and divide by the target factor. Example: a 250 US GPM pump × 0.227125 = 56.78 m³/h.
Where flow conversion is used
- Pump selection: reading imported pump curves in GPM against plant design flows in m³/h.
- HVAC airflow: converting fan and air handler CFM into m³/h or L/s for air-change checks.
- Water and effluent treatment: putting dosing pumps, filters and membrane skids on one unit before summing capacity.
- Fire and drainage: switching between L/s and m³/h for code documentation.
Mistakes to avoid
- L/s vs L/min: a factor of 60 error that is easy to make when reading a datasheet quickly.
- US vs imperial gallon: an imperial gallon is 4.54609 L, about 20% larger than the US gallon used here.
- Mass or standard flow: kg/h, SCFM and Nm³/h depend on density, temperature and pressure, so they are not simple unit conversions.
Frequency & Rotational Speed Converter: Hz, kHz, MHz, GHz, THz, RPM, rad/s and °/s
Base unit: hertz (Hz)RPM = Hz × 60ω = 2π × f
This converter covers the SI hertz scale (Hz to THz) and cycles per second, together with rotational speed units (RPM, rad/s, °/s). RPM is not an SI frequency unit; it is linked to hertz here on the basis of one cycle per revolution. It is useful for VFD settings, motor and generator speeds, instrumentation and signal specifications.
Frequency conversion table
| 1 unit | Hz | RPM | rad/s | °/s |
|---|
| 1 Hz (1 cps) | 1 | 60 | 6.283185 | 360 |
| 1 kHz | 1,000 | 60,000 | 6,283.185 | 360,000 |
| 1 RPM | 0.016667 | 1 | 0.104720 | 6 |
| 1 rad/s | 0.159155 | 9.549297 | 1 | 57.29578 |
| 1 °/s | 0.002778 | 0.166667 | 0.017453 | 1 |
Frequency formulas
- Period: f = 1 ÷ T. A 50 Hz waveform has a period of 0.02 s (20 ms).
- Waves: f = v ÷ λ, where v is wave velocity and λ is wavelength.
- Rotation: 1 Hz = 60 RPM = 2π rad/s = 360 °/s, for one cycle per revolution.
- Synchronous speed: Ns = (120 × f) ÷ P. A 4-pole machine runs at 1,500 RPM on 50 Hz and 1,800 RPM on 60 Hz; induction motors run slightly slower because of slip.
50 Hz and 60 Hz grids by region
| Grid frequency | Examples |
|---|
| 50 Hz | Most of Europe, Asia and Africa; Australia and New Zealand; much of South America, such as Argentina and Chile |
| 60 Hz | North America (United States, Canada, Mexico); Brazil, Colombia and Peru; South Korea, Taiwan and the Philippines; Saudi Arabia |
| Both | Japan: eastern Japan 50 Hz, western Japan 60 Hz |
Unit converter vs electrical frequency converter
- This tool: changes how a frequency is written, such as Hz to RPM.
- Static frequency converter: power equipment with a rectifier (AC to DC) and inverter (DC to new AC frequency).
- Rotary frequency converter: a motor-generator set; the generator's speed and poles set the output frequency, and its rotating mass rides through very short disturbances.
- Special frequencies: 400 Hz aircraft ground power, 16.7 Hz rail traction in Germany, Austria, Switzerland, Sweden and Norway, and 25 Hz on parts of the US Northeast Corridor.
Running equipment on the other frequency
- Electronics: many chargers and switch-mode supplies are rated “50/60 Hz”; check the nameplate.
- 50 Hz motor on 60 Hz: about 20% faster at the same voltage, so fan and pump loads can draw much more power.
- 60 Hz motor or transformer on 50 Hz: higher magnetic flux, magnetizing current and heating unless voltage is reduced in the same ratio.
Speed Converter: m/s, km/h, mph, knot and ft/s
Base unit: meter per second (m/s)1 knot = 1.852 km/h
The speed converter switches between m/s, km/h, miles per hour, knots and feet per second for conveyors, fluid velocity, fans, wind and marine data. All factors follow exact unit definitions.
Speed conversion factors
| Unit | In m/s | 1 m/s equals |
|---|
| 1 km/h | 1 ÷ 3.6 ≈ 0.277778 | 3.6 km/h |
| 1 mph | 0.44704 (exact) | ≈ 2.23694 mph |
| 1 knot | 1,852 ÷ 3,600 ≈ 0.514444 | ≈ 1.94384 knots |
| 1 ft/s | 0.3048 (exact) | ≈ 3.28084 ft/s |
How to convert speed
Multiply by the m/s factor of the starting unit and divide by the target factor. Example: 100 km/h ÷ 3.6 = 27.778 m/s = 62.137 mph.
Where speed conversion is used
- Conveyors and fluid velocity: comparing m/s design values with ft/s ratings on imported equipment.
- Wind data: checking turbine cut-in speeds in m/s or mph against weather data in km/h or knots.
- Marine and offshore: converting design wind or current speeds from knots to m/s for load calculations.
- Fan and wheel tip speed: v (m/s) = π × D × N ÷ 60, with D in meters and N in RPM. A 0.5 m fan at 1,450 RPM has a tip speed of about 37.96 m/s.
Mistakes to avoid
- Knot vs mph: a knot is about 15% faster than 1 mph.
- Radius instead of diameter: using radius in π × D × N ÷ 60 halves the tip speed and hides an overspeed risk.
