How much water does each grass type need?
Different turf species lose different amounts of water to evaporation and transpiration even under identical weather, because leaf shape, root depth and photosynthesis differ by species. Research summarized by the University of California groups common lawn grasses into five water-use categories based on their peak-season evapotranspiration (ET) rate in full sun, and separately rates their drought resistance from very poor to superior.
Warm-season grasses (bermudagrass, zoysiagrass, St. Augustinegrass, buffalograss and similar) generally use noticeably less water than cool-season grasses (tall fescue, Kentucky bluegrass, perennial ryegrass) during the growing season, because their photosynthetic pathway keeps producing carbohydrate even when their stomata partly close to conserve water.
| Grass type | Season | Water use | Weekly range (full sun) | Drought resistance |
|---|---|---|---|---|
| Buffalograss | Warm | Very low | under 1.68 in (43 mm) | Superior |
| Bermudagrass | Warm | Low | 1.68\u20131.96 in (43\u201350 mm) | Superior |
| Zoysiagrass | Warm | Low | 1.68\u20131.96 in (43\u201350 mm) | Excellent |
| Seashore paspalum | Warm | Medium | 1.96\u20132.31 in (50\u201359 mm) | Excellent |
| St. Augustinegrass | Warm | Medium | 1.96\u20132.31 in (50\u201359 mm) | Good |
| Kikuyugrass | Warm | High | 2.31\u20132.73 in (59\u201369 mm) | Good |
| Fine fescue | Cool | Medium | 1.96\u20132.31 in (50\u201359 mm) | Fair |
| Perennial ryegrass | Cool | High | 2.31\u20132.73 in (59\u201369 mm) | Fair |
| Tall fescue | Cool | Very high | over 2.73 in (69 mm) | Medium |
| Kentucky bluegrass | Cool | Very high | over 2.73 in (69 mm) | Fair |
| Creeping bentgrass | Cool | Very high | over 2.73 in (69 mm) | Fair |
Creeping bentgrass is included for completeness but is a specialty, very-low-mow grass used mainly on golf greens, not a typical home lawn.
Check local rules first. Many water utilities set watering days, hours or weekly limits. Where those apply, they take priority over any calculated amount.
How this calculator works
The calculator starts from your species' published water-use category, converts it to a weekly range, then layers on a season adjustment and a shade adjustment. If you enter your lawn area, it also converts the adjusted range into gallons or liters.
1. Species baseline
Weekly range from the ET-rate category
Weekly range (in) = Daily ET-rate category bounds (in/day) \u00d7 7
Category bounds come from Table 1 of University of California ANR Publication 8395 (adapted from Beard and Beard 2004). Open-ended categories (\u201cvery low,\u201d \u201cvery high\u201d) stay open-ended after conversion.
2. Season adjustment
Typical seasonal multiplier
Adjusted range = Weekly range \u00d7 season factor (0.7 cool, 1.0 typical, 1.3 hot)
These are general planning multipliers, not a published per-species figure \u2014 treat them as typical, and adjust based on how your lawn actually looks.
3. Shade adjustment
Shade factor
Shaded range = Adjusted range \u00d7 0.5 (if shaded most of the day)
University of California Cooperative Extension documented this roughly 50% reduction for turf in full shade during hot summer months.
4. Convert to gallons or liters (optional)
US units
Gallons = Area (sq ft) \u00d7 Depth (in) \u00d7 0.623
One inch of water over one square foot is 144 cubic inches, and a US gallon is 231 cubic inches. 144 \u00f7 231 \u2248 0.623.
Metric units
Liters = Area (m\u00b2) \u00d7 Depth (mm)
One millimeter of water over one square meter is exactly one liter.
Rounding
Depths are shown to 2 decimals in US units and 1 decimal in metric, matching the precision used in the math. Gallon and liter figures are estimates built on a typical category, so they're rounded and shown with "about."
When this calculator isn't the right tool
It gives a typical, weather-independent range for a species. Use a different tool for:
- This week's actual watering amount, which depends on measured rainfall and your weekly target. See the lawn watering calculator.
- An evapotranspiration-based figure tied to your local weather station data. See the lawn water requirement calculator.
- New grass seed or sod, which need frequent light watering, not a weekly depth. See the grass seed watering calculator or sod watering calculator.
- Sprinkler run times for a given depth. See the how long to water lawn calculator.
Worked example
A homeowner has a 5,000 sq ft bermudagrass lawn in full sun during a typical growing-season week.
- Species category: Bermudagrass is "low," 0.24\u20130.28 in/day.
- Weekly range: 0.24 \u00d7 7 = 1.68 in; 0.28 \u00d7 7 = 1.96 in.
- Season factor: Typical growing season \u00d7 1.0 \u2014 range unchanged: 1.68\u20131.96 in/week.
- Shade factor: Full sun \u00d7 1.0 \u2014 range unchanged.
- Gallons: 5,000 \u00d7 1.68 \u00d7 0.623 \u2248 5,233, shown as about 5,230 gal; 5,000 \u00d7 1.96 \u00d7 0.623 \u2248 6,105, shown as about 5,230\u20136,110 gallons.
The same calculation in metric
A zoysiagrass lawn, full sun, typical growing season, no area entered:
- Species category: Zoysiagrass is "low," 0.24\u20130.28 in/day = 6.10\u20137.11 mm/day.
- Weekly range: 6.10 \u00d7 7 = 42.7 mm; 7.11 \u00d7 7 = 49.8 mm.
- Season and shade factors: both \u00d7 1.0 \u2014 range unchanged: 42.7\u201349.8 mm/week.
An edge case: cool season, shaded buffalograss
Buffalograss is "very low" (under 0.24 in/day), with no published lower bound. In cool spring/fall (\u00d70.7) and full shade (\u00d70.5), the calculator shows only the open upper bound: 0.24 \u00d7 7 \u00d7 0.7 \u00d7 0.5 = 0.588, displayed as under 0.59 in/week. The other end, a hot, sunny week of tall fescue, shows only a floor: 0.39 \u00d7 7 \u00d7 1.3 = 3.549, displayed as more than 3.55 in/week. Open-ended source categories stay open-ended \u2014 the calculator never invents a ceiling or floor that wasn't published.
Using this estimate on your lawn
Identify your grass first
If you're not sure what you have, look at growth pattern and season: warm-season grasses spread by stolons or rhizomes and typically turn tan and go dormant after the first frost, while cool-season grasses stay green through winter in most of the US and slow down in summer heat instead. A seed bag, sod invoice, builder's landscape plan, or your county extension office can confirm the species or cultivar.
Rate your sun and shade honestly
"Shaded most of the day" means tree canopy or building shadow for a large part of daylight hours, not just morning or evening shade. A lawn with dappled, partial shade sits somewhere between the two figures shown \u2014 lean toward the shaded number if the shade is heavy, or the full-sun number if it's light.
Common mistakes
- Treating the range as a fixed target. It's a starting point; actual need still depends on your specific weather, soil and how the lawn looks.
- Ignoring rainfall. This range is gross water need, not what to add after rain. Subtract measured rainfall using the lawn watering calculator.
- Guessing the species. Bermudagrass and zoysiagrass can look similar at a glance but have different mowing heights and blade textures; check before assuming.
- Applying the full-sun number to a shaded backyard. That typically overwaters shaded turf and can encourage fungal disease.
What changes the result
| Factor | Effect on water need | What to adjust |
|---|---|---|
| Species | Sets the baseline category, from "very low" to "very high." | Confirm the species before relying on the range. |
| Sun vs. shade | Shaded turf uses roughly half as much water in hot weather. | Select "Shaded" for areas under heavy tree or building shade. |
| Season | Heat, sun and wind raise water loss; cool, cloudy weather lowers it. | Move toward "Hot, dry, windy" in peak summer, "Cool spring/fall" in shoulder seasons. |
| Soil type | Sets how much water the root zone holds and how fast it drains. | Sandy soils need more frequent, smaller applications; clay needs fewer, longer soaks split into cycles. |
| Mowing height | Taller turf generally has deeper roots and a more open canopy, raising water use. | Mow at the top of the recommended range for your species rather than very short. |
| Rainfall | Reduces how much irrigation is needed that week. | Use the lawn watering calculator to subtract measured rain. |
| Cultivar | Water use varies between cultivars of the same species. | Treat the species range as a starting point, not an exact figure. |
Frequently asked questions
How much water does Bermuda grass need per week?
University of California research places bermudagrass in the "low" water-use category, with a reference evapotranspiration rate of about 0.24 to 0.28 inches per day in full sun during active growth, which works out to roughly 1.68 to 1.96 inches per week before any season or shade adjustment. Bermudagrass also has "superior" drought resistance, so it can go dormant in dry spells and usually recovers once watering resumes.
How much water does zoysia grass need?
Zoysiagrass shares bermudagrass's "low" water-use category in University of California research, roughly 1.68 to 1.96 inches per week in full sun during active growth. Its drought resistance is rated "excellent," one step below bermudagrass's "superior" rating, so it holds up well in dry weather but may thin out slightly sooner under prolonged drought.
How much water does tall fescue need per week?
Tall fescue falls in the "very high" water-use category, with a reference evapotranspiration rate above 0.39 inches per day in full sun, or more than about 2.73 inches per week before adjustment \u2014 the highest of the common lawn grasses. Its drought resistance is rated "medium," helped by roots that can reach 1.5 to 3 feet deep, deeper than most other cool-season lawn grasses.
How much water does St. Augustine grass need?
St. Augustinegrass sits in the "medium" water-use category, about 0.28 to 0.33 inches per day in full sun, or roughly 1.96 to 2.31 inches per week before adjustment. Its drought resistance is rated "good": it doesn't avoid water loss as well as bermudagrass, but its tissue tolerates dehydration better, so it wilts before it dies back.
Which grass type uses the least water?
Among species with published University of California data, buffalograss uses the least, in the "very low" category at under 0.24 inches per day, and it also carries a "superior" drought-resistance rating. Bermudagrass and zoysiagrass follow closely in the "low" category. All three are warm-season grasses; cool-season lawns such as tall fescue and Kentucky bluegrass use noticeably more.
Does shade really cut my lawn's water need in half?
During hot summer months, University of California Cooperative Extension found that turfgrass grown in full shade typically needs about half as much water as the same grass in full sun, and this calculator applies that factor when you select "Shaded." That figure was documented specifically for hot summer conditions; shade likely saves proportionally more in cooler months, though there isn't a published exact number for that case.
Do I need to water more in hot, dry, windy weather?
Yes, water loss from grass rises with heat, sun and wind. This calculator applies a general seasonal adjustment on top of each species' baseline range, but that adjustment is a typical planning figure rather than a species-specific published number.
For a precise, weather-driven figure, use the lawn water requirement calculator, or check with your local extension office.
Can I subtract this week's rainfall to get a gallons figure?
Not with this tool. It estimates a typical weekly range for your species, season and light, not a rainfall-adjusted total for one specific week.
To subtract measured rain and get a gallons figure, use the lawn watering calculator, which is built around that weekly water balance.
Who built and checked this calculator
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- Species water-use and drought-tolerance categories checked against the University of California source table.
- Unit conversions and both worked examples verified by hand, including the open-ended edge case.
- Season and shade adjustments are clearly labeled as typical, not attributed to a specific published per-species figure.
Sources
- Harivandi, M.A., Baird, J., Hartin, J., Henry, M., Shaw, D. University of California Division of Agriculture and Natural Resources. Managing Turfgrasses during Drought (ANR Publication 8395). [VERIFY URL]
- Rutgers Cooperative Extension. Best Management Practices for Watering Lawns (FS555).
- Clemson Cooperative Extension, Home & Garden Information Center. How Often Should A Lawn Be Watered?
- NC State Extension Publications. Water Requirements of North Carolina Turfgrasses.
- Huang, B. United States Golf Association. Turfgrass Water Requirements and Factors Affecting Water Usage.