Lawn
How much and how long to water established lawns, new seed and sod.
All 11 Lawn calculatorsIrrigation Calculators
Free tools that show their work.
Work out how much to water, how long to run sprinklers and drip, what size pipe you need, and how much water your crops use. Every calculator uses an established engineering method and shows its formula, assumptions and sources.
Built and reviewed by Daniel Reeves, PE, CID, a licensed Professional Engineer and Certified Irrigation Designer with more than 20 years in irrigation design.
Quick lawn estimate
Water for one week at about 1 inch (25 mm), a common starting point for established lawns.
Formula: area × 1 in × 0.623 = US gallons (area × 25 mm = liters). Estimate only; needs vary with weather, soil and grass type.
Calculators by category
From a backyard lawn to a center pivot
Ten categories of irrigation and watering calculators. Each tool answers one specific question, in US or metric units.
Sprinklers
Precipitation rates, run times, spacing, zones, audits and winterizing.
All 17 Sprinklers calculatorsDrip Irrigation
Emitters, run times, zone flow, tubing layout, pressure and filtration.
All 17 Drip Irrigation calculatorsIrrigation Hydraulics
Pipe sizing, friction loss, velocity, pressure and supply flow.
All 14 Irrigation Hydraulics calculatorsScheduling & ET
Evapotranspiration, water requirements, schedules and water budgets.
All 16 Scheduling & ET calculatorsSoil & Water Quality
Water holding capacity, infiltration, moisture, salinity and sodium.
All 10 Soil & Water Quality calculatorsAgriculture
Crop water needs, system capacity, set times, pivots and field systems.
All 16 Agriculture calculatorsGarden & Trees
Beds, vegetables, containers, trees, shrubs, greywater and rainwater.
All 9 Garden & Trees calculatorsFertigation
Injection rates, stock solutions and fertilizer concentrations.
All 6 Fertigation calculatorsCost & Savings
Water costs, system costs and savings from upgrades.
All 8 Cost & Savings calculatorsStart with your question
What are you trying to work out?
The most common irrigation questions, each answered by a calculator built for it.
- How much water does my lawn need this week?
- How long should I run my sprinklers?
- How many sprinkler heads can go on one zone?
- What size pipe do I need for my flow?
- How long should I run my drip system?
- How much water does my crop need this season?
- How much water does a tree need?
- What does watering my lawn cost?
Why you can trust the numbers
Every answer comes with its working
A calculator is only useful if you can trust it. So every one of ours shows you exactly how it got there.
Established methods
Formulas come from FAO, USDA NRCS, the Irrigation Association, ASABE and university extension. Nothing is invented.
Formulas on the page
Each calculator shows its formula and a worked example that matches the tool, so you can check any result.
Assumptions stated
Every result lists the assumptions behind it, and they travel with it when you copy, download or print.
Engineer reviewed
Methods, formulas and sourced values are reviewed by a licensed Professional Engineer before a page is published.
Formula
Gallons = Area (sq ft) × Depth (in) × 0.623
One inch over one square foot is 144 cubic inches; a US gallon is 231. 144 ÷ 231 ≈ 0.623.
- Lawn area5,000 sq ft
- Weekly target1 in
- Calculation5,000 × 1 × 0.623
About 3,120 gallons per week
Shown as an estimate, rounded to the nearest 10 gallons, with its assumptions listed. Try the full calculator.
Who it's for
Built for homeowners and professionals
Clear enough for a first-time gardener, rigorous enough for an irrigation auditor.
Homeowners
How much and how long to water your lawn and garden, how to set your timer, and what your watering costs.
Lawn calculators →Landscape and irrigation contractors
Precipitation rates, zone flows, head spacing and run times you can check on site and explain to clients.
Sprinkler calculators →Irrigation designers and auditors
Pipe sizing, pressure budgets, uniformity and water budgets, with the method and source stated every time.
Hydraulics calculators →Farm managers and growers
Crop water requirements, system capacity, set times, pivots, drip tape and fertigation, in acre-inches or metric.
Agriculture calculators →The engineer behind the calculators
Built by an irrigation engineer, not a template
Daniel Reeves, PE, CID
Irrigation Design Engineer & Water-Efficiency Specialist
- Licensed Professional Engineer
- Certified Irrigation Designer (IA)
- B.S. Civil Engineering
- 20+ years
Daniel spent a decade designing and commissioning irrigation systems for parks, golf courses, HOAs and large residential properties, then carried out hundreds of irrigation audits as a water-efficiency specialist for a municipal water agency.
He develops, validates and reviews every calculator and reference chart on this site. Read his full profile or see our methodology and editorial policy.
Reference charts
The data behind the calculators
Authoritative irrigation data in one place, transcribed from the original sources and checked value by value.
- Crop coefficient tableFAO-56 Kc values for 125 crops
- Sprinkler precipitation rate chartRates by head type, flow and spacing
- Soil infiltration rate chartIntake rates by soil type and slope
- PVC friction loss chartSchedule 40 and Class 200, 1–150 GPM
- Lawn watering by grass typeWater needs of 13 lawn grasses
Our sources
Built on published science and standards
We use sources in this order, and name them on every page.
International and government
FAO Irrigation and Drainage Papers, and USDA Natural Resources Conservation Service handbooks and standards.
Professional bodies
Irrigation Association practice and ASABE engineering standards.
University extension
Research-based guidance from extension services such as University of California, Colorado State and Rutgers.
Manufacturer data
Published specifications, used only for equipment-specific values and always named.
Questions
Frequently asked questions
Are these irrigation calculators free?
Yes. Every calculator and reference chart on the site is free to use, with no account, sign-up or paywall.
How accurate are the results?
Each calculator uses an established method from sources such as FAO, USDA NRCS, the Irrigation Association or university extension, and shows its formula and a worked example. Results are planning estimates: they're only as good as the values you enter, and each page lists the assumptions behind its result.
Who builds and checks the calculators?
The calculators and reference data are developed and reviewed by Daniel Reeves, PE, CID, a licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design and water-efficiency auditing.
Do the calculators work in metric units?
Yes. Every calculator works in US customary and metric units. When you switch, the values you've already entered are converted and the result stays the same.
Do you store the values I enter?
No. Calculations run in your browser, and the values you enter aren't sent to us. If you use a calculator's share link, your values are included in the link's web address so the calculator can reopen with them.
Can I use the results to design an irrigation system?
The calculators are built for planning, checking and everyday decisions. For large, commercial or agricultural systems, use them as a starting point and have the design completed by a qualified irrigation designer or engineer who can assess the site.
Find the right calculator
Browse every irrigation and watering calculator by category, or tell us about a tool you'd like us to build.