Conversion from Cubic inches per minute to US Gallons per hour

Information about the Cubic inch per minute (in³/min)

The cubic inch per minute is a unit of volumetric flow rate equal to one cubic inch passing a point every minute. Its symbol is in³/min. In the machine shop it is better known by its initials: MRR, the material removal rate, the single figure that says how fast a cutting process is turning solid metal into chips.

The calculation behind it is simple multiplication. Depth of cut times width of cut times feed rate gives the volume removed per minute, so a 0.2-inch depth at 1 inch wide with a feed of 30 inches per minute removes 6 cubic inches per minute. Every variable a machinist can change appears in that product, which is why it is the number used to compare one strategy against another.

Material decides what is achievable. Roughing aluminium on a rigid machine can exceed 100 cubic inches per minute, mild steel manages perhaps 10 to 20, stainless steel less, and nickel alloys used in turbine parts only a few. The limit is set by spindle power, by the rigidity of the setup and by the heat the tool can survive, in whichever order runs out first.

Spindle power connects directly to it. Each material has a specific cutting energy, roughly 1 horsepower per cubic inch per minute for steel and a third of that for aluminium, so a 20-horsepower spindle can sustain about 20 cubic inches per minute in steel. A quoted removal rate that exceeds the machine's power is arithmetic that the machine will settle in its own way.

Beyond cutting, the unit describes small imperial flows generally. Hydraulic pilot lines, lubrication systems, fuel injection test benches and adhesive dispensers on American equipment are all rated in cubic inches per minute, where the metric world would say millilitres per minute.

For scale, 61 cubic inches per minute is about a litre per minute, and 231 cubic inches per minute is exactly one US gallon per minute — the gallon being defined as 231 cubic inches. That exact relation is why hydraulic engineers move between the two units without a conversion table.

One cubic inch per minute equals about 16.39 cubic centimetres per minute, about 0.01667 cubic inches per second, or about 0.004329 US gallons per minute.

Information about the US Gallon per hour (gal US/h)

The US gallon per hour is a unit of volumetric flow rate equal to one United States gallon passing a point every hour. Its symbol is gal US/h, commonly abbreviated GPH. At 3.785 litres to the gallon, an hour at this rate delivers a little under four litres, which places it among the slow, continuous flows of heating, irrigation and fuel systems.

Drip irrigation is its most familiar use in America. Emitters are sold rated at 0.5, 1 and 2 gallons per hour, and a garden bed is designed by choosing an emitter for each plant and multiplying by the number of plants. A zone of two hundred one-gallon emitters draws 200 gallons per hour, and a two-hour cycle applies 400 gallons — figures a homeowner can check against the water bill.

Oil burners are rated in it in the United States, exactly as in Britain. A residential oil furnace carries a nozzle marked 0.75 or 1.00 gallons per hour, and multiplying by about 140,000 British thermal units per gallon gives the burner's firing rate. The nozzle is thus both a fuel metering device and the effective rating plate of the appliance.

Water heaters and small appliances follow. A tankless water heater's recovery, an ice machine's water consumption, a humidifier's evaporation rate and a coffee urn's draw are all commonly expressed in gallons per hour, since these appliances run more or less continuously and are chosen to match a daily demand.

Fuel consumption of engines under steady load is quoted this way in American practice. A generator burns 0.5 to 3 gallons per hour depending on size and load, a boat's engine several, and a large marine diesel dozens. Dividing the tank capacity by the hourly rate gives the endurance, which for a boat is the number that actually matters.

For scale, one US gallon per hour is about 3.79 litres per hour, and 264 gallons per hour is about a cubic metre per hour. Sixty gallons per hour is one gallon per minute, so the two American flow units are connected by the same factor that connects the minute to the hour.

One US gallon per hour equals about 3.785 litres per hour, about 0.003785 cubic metres per hour, or about 0.8327 imperial gallons per hour.