Hose · calculator
Garden Hose Flow Rate Calculator: GPM by Length & PSI
Estimate water flow through a garden hose from pressure, actual inside diameter, length, and friction coefficient.
Method record
What this calculator measures
Diameter has a strong nonlinear effect on hose capacity. A nominal 5/8-inch hose should not be assumed to have an exact 0.625-inch flow passage without checking the product.
Q = [ΔP × C¹·⁸⁵ × d⁴·⁸⁷ ÷ (4.52 × L)]¹/¹·⁸⁵ Use it correctly
Calculation steps
- Measure pressure while the outlet is flowing.
- Use actual hose inside diameter and total length.
- Account separately for nozzles, reels, connectors, and elevation.
Applicability
Use the model within its limits
Hazen-Williams is an estimate. A bucket test captures all real restrictions in the assembled hose system.
What this result represents
- System
- Hose
- Formula
- Q = [ΔP × C¹·⁸⁵ × d⁴·⁸⁷ ÷ (4.52 × L)]¹/¹·⁸⁵
- Review
- Verify safety-sensitive work with qualified guidance.
Worked Field Example
Worked Example: 100-Foot Garden Hose Discharge
Field Scenario: Estimating actual discharge flow from a standard 100-foot, 5/8-inch garden hose connected to an outdoor sillcock at 50 PSI supply pressure.
Given Input Parameters
Step-by-Step Mathematical Solution
- Accounting for sillcock globe valve restriction and open end discharge, effective dynamic pressure drop is ~42 PSI.
- Solve Hazen-Williams flow formula: Q = [(42 × 140^1.852 × 0.625^4.87) / (4.52 × 100)]^(1/1.852).
- Q ≈ 7.1 GPM with an exit velocity of 7.4 ft/s.
Approximately 7.1 GPM open discharge flow rate.
Professional Guidance: Upgrading to a 3/4-inch hose increases open flow from 7.1 GPM to approximately 11.5 GPM at the same spigot pressure.
Engineering Standard Reference
Garden Hose Flow Rate Benchmarks & 5-Gallon Bucket Timing Chart
Realistic water discharge flow rates and bucket fill times for standard garden hoses at typical residential spigot pressures (40 to 60 PSI):
| Hose Inside Diameter | Hose Length | Flow @ 40 PSI | Flow @ 50 PSI | Flow @ 60 PSI | 5-Gallon Bucket Time |
|---|---|---|---|---|---|
| 1/2" (Light Duty) | 25 ft | 6.5 GPM | 7.3 GPM | 8.0 GPM | ~38–46 sec |
| 1/2" (Light Duty) | 50 ft | 5.2 GPM | 5.8 GPM | 6.4 GPM | ~47–58 sec |
| 1/2" (Light Duty) | 100 ft | 4.0 GPM | 4.5 GPM | 4.9 GPM | ~61–75 sec |
| 5/8" (Standard) | 25 ft | 12.0 GPM | 13.5 GPM | 14.8 GPM | ~20–25 sec |
| 5/8" (Standard) | 50 ft | 9.5 GPM | 10.7 GPM | 11.7 GPM | ~26–32 sec |
| 5/8" (Standard) | 100 ft | 7.2 GPM | 8.1 GPM | 8.9 GPM | ~34–42 sec |
| 3/4" (Commercial) | 25 ft | 19.5 GPM | 21.8 GPM | 23.9 GPM | ~13–15 sec |
| 3/4" (Commercial) | 50 ft | 15.0 GPM | 16.8 GPM | 18.4 GPM | ~16–20 sec |
| 3/4" (Commercial) | 100 ft | 11.8 GPM | 13.2 GPM | 14.5 GPM | ~21–25 sec |
Engineering Note: Rates assume unrestricted open-end discharge. How to do the 5-Gallon Bucket Test: Fill a 5-gal bucket with wide-open hose, time seconds with stopwatch, then calculate: GPM = (5 ÷ Seconds) × 60.
Engineering FAQs
Frequently Asked Questions
Why is actual garden hose flow much lower than outdoor spigot static pressure suggests?
Small-diameter hoses create severe friction losses over long distances. At 10 GPM, a 5/8-inch hose loses over 0.5 PSI per linear foot. Over 100 feet, friction alone consumes 50+ PSI of energy.
How much more water does a 3/4-inch hose deliver compared to a 5/8-inch hose?
A 3/4-inch hose has an inside area ~44% larger than a 5/8-inch hose and delivers roughly 60% to 80% more flow at identical supply pressure due to the inverse 4.87 power dependence of friction on diameter.
Does hose nozzle restriction increase or decrease total flow?
Nozzle restrictions increase discharge velocity (creating a high-speed jet) but decrease the total volumetric flow (GPM) by creating downstream backpressure that throttles flow through the hose.