Gallons Per Hour Calculator

Calculate gallons per hour from a volume and time, or convert GPH to GPM and liters per hour and back; also find volume or time from a flow rate.

• All Unit Converters
• Gallons Per Minute Calculator
• Volumetric Flow Rate Calculator
• Water Flow Rate Calculator
• CFS to GPM Calculator
• Gallons Per Minute to Cubic Feet Per Second Calculator
• Hose Flow Rate Calculator

Calculator Functions

Function	What it does	What it requires
Flow rate	Finds the flow rate in gallons per hour from an amount of liquid and the time it took	Requires the liquid volume and the elapsed time
Liquid volume	Finds how many gallons flow in a given time	Requires the flow rate and the elapsed time
Elapsed time	Finds how long a volume takes to flow, fill or drain	Requires the liquid volume and the flow rate
Convert GPH, GPM or L/h	Converts a flow rate between gallons per hour, gallons per minute, gallons per day and liters per hour or minute	Requires a flow rate and its unit

Volumes go in as US gallons, Imperial gallons, liters, cubic meters or cubic feet. Time goes in as seconds, minutes, hours or days. Flow rates go in as US gal/h, US gal/min, US gal/day, Imperial gal/h, L/h, L/min or m³/h. Answers come out in US gallons and hours, with liters and other units listed below the main result.

Gallons Per Hour Formulas

Flow rate

The volume is divided by the time, after both are converted to US gallons and hours. A 275.2 gallon pool filled in 8.6 hours took 275.2 ÷ 8.6 = 32 GPH. A 5 gallon bucket filled in 2 minutes is 5 ÷ (2 ÷ 60) = 150 GPH.

Liquid volume

The flow rate is multiplied by the time. A pump running at 32 GPH for 2.5 hours moves 80 gallons, which is 302.83 L.

Elapsed time

The volume is divided by the flow rate. Emptying 1,200 gallons at 32 GPH takes 1,200 ÷ 32 = 37.5 hours. A flow rate of zero is rejected.

Convert GPH, GPM or L/h

An hour has 60 minutes and a day has 24 hours, so GPM = GPH ÷ 60 and gallons per day = GPH × 24. A flow of 304 GPM is 18,240 GPH, and 2,880 gallons per day is 120 GPH. One US gallon is 3.785412 L and one Imperial gallon is 4.54609 L [1], so L/h = GPH × 3.785412 and 200 L/h is 52.83 GPH. An Imperial gallon per hour is 1.20095 US gallons per hour.

GPH	GPM	L/h	Gallons per day
1	0.0167	3.79	24
5	0.0833	18.93	120
10	0.1667	37.85	240
20	0.3333	75.71	480
50	0.8333	189.27	1,200
100	1.6667	378.54	2,400
200	3.3333	757.08	4,800
500	8.3333	1,892.71	12,000
1,000	16.6667	3,785.41	24,000

Limits of This Estimate

• The flow rate is an average over the time entered. A pump or tap that speeds up, slows down or stops part of the way through has a different rate at any given moment.
• Results are in US liquid gallons. An Imperial gallon is about 20% larger, so a rating in Imperial gallons has to be entered with that unit.
• The calculation relates volume and time only. It does not find the flow through a pipe from its size or pressure, and a pump’s rated GPH falls as it lifts water higher.

Sources