Free Wind Rose Generator
Directions are where the wind blows from, clockwise from north.
A wind rose shows where the wind comes from, how often and how strongly. Pick a city or type coordinates, load a year of hourly wind from NASA POWER, or open an EPW or CSV file, and this wind rose generator draws a chart ready for your site analysis board. It is free, there is no sign up, and a file you open is read in your browser, never uploaded.
How to use this wind rose generator
- Set the site. Choose a city from the list, or type the latitude and longitude. North and east are positive, south and west are negative. Any point on land or sea works; the city list is only a shortcut.
- Load the wind. Pick a year, from 2001 to the current year, and press Load wind data. The generator fetches every hour of that year from NASA POWER and keeps a copy in your browser, so the same place and year open again from that copy without a new request. The current year is loaded up to the latest available data and the chart says which dates it covers. To use your own records, switch the source to an EPW weather file or a CSV file.
- Set the chart. Choose 16 sectors of 22.5° or 8 sectors of 45°, and the speed unit: m/s, km/h, mph, knots or the Beaufort scale. Set the calm limit and the speed class limits, and choose whether the spokes show frequency in percent of the time or duration in hours.
- Filter by time. Show the whole year, one of the four three month seasons or months you pick yourself, and limit the hours of the day if you want, for example from 20:00 to 06:00 for night winds.
- Export. PNG is drawn at 2000 px wide for slides, SVG stays sharp on a presentation board, and CSV gives you the full table of directions and speed classes. You can export in light or dark colours, or print the tool on its own. The location you choose is carried over to the climate graph and bioclimatic chart tools.
What a wind rose tells an architect
The longest spoke is the prevailing wind: the direction the wind blows from most often. Look next for a secondary spoke, often roughly opposite, which in many places belongs to a different season or a different weather pattern. Then look at the number in the centre, the calm share, which tells you how often there is effectively no wind to work with.
Those three readings feed straight into early design decisions.
- Openings and cross ventilation. Openings that face the summer breeze, with outlets on the opposite side, let the wind cross the plan. A high calm share in summer means you cannot rely on the wind, and stack ventilation has to do more of the work. Our guide to designing for natural ventilation in warm climates covers the layouts.
- Entrances and outdoor space. Keep main entrances, terraces and playgrounds out of the cold winter wind, and put courtyards where the building shelters them.
- Windbreaks. Planting, walls and secondary buildings belong on the side of the strong cold winds, which the speed classes in the outer part of each spoke make easy to spot.
- Smells, smoke and noise. Anything you do not want carried across the site, such as a car park, bins or a kitchen extract, belongs downwind of the spaces you use most.
How to read this wind rose
Directions follow the meteorological convention: a spoke points to the direction the wind blows from, measured clockwise from true north. A north wind blows from the north towards the south. With 16 sectors each spoke covers 22.5°, so the north sector runs from 348.75° to 11.25°.
Each spoke is split into coloured segments, one per speed class, from the lightest winds near the centre to the strongest at the tip. The rings carry their values, in percent or in hours, along the emptiest direction so they do not cover the data. In frequency mode every value is a share of all valid hours, calms included, so all the spokes plus the calm share add up to 100%.
Calms are hours below the calm limit. They have no meaningful direction, so they are not put in any spoke; they are counted on their own and printed in the centre circle and in the legend. Under the chart you also get the prevailing direction with its share, the mean and highest speed, the number of calm hours, the number of valid hours and, if the data had gaps, how many missing values were skipped.
Speed classes and the Beaufort scale
The default speed classes are 2, 4, 6, 8 and 10 m/s, and you can type up to ten limits of your own. They must increase, and the first one must be above the calm limit. Each unit has its own sensible defaults: 5, 10, 20, 30 and 40 km/h, 5, 10, 15, 20 and 25 mph, and 4, 7, 11, 17 and 22 knots.
The calm limit is always set in m/s, 0.5 m/s by default, whatever unit you show. When you switch units, the class limits are converted and only the labels change: no hour moves to a different class, so the rose and the calm share stay exactly the same. If you then type new limits, the numbers you type are used.
As a feel for the numbers: around 2 m/s you feel the wind on your face and leaves rustle. Around 4 m/s leaves and small twigs are in constant motion and a light flag extends. Around 6 m/s the wind raises dust and loose paper and small branches move. Choose the Beaufort scale and the classes switch to Beaufort forces, using these limits in m/s.
| Force | Description | Wind speed (m/s) |
|---|---|---|
| 0 | Calm | below 0.3 |
| 1 | Light air | 0.3 to 1.5 |
| 2 | Light breeze | 1.6 to 3.3 |
| 3 | Gentle breeze | 3.4 to 5.4 |
| 4 | Moderate breeze | 5.5 to 7.9 |
| 5 | Fresh breeze | 8.0 to 10.7 |
| 6 | Strong breeze | 10.8 to 13.8 |
| 7 | Near gale | 13.9 to 17.1 |
| 8 | Gale | 17.2 to 20.7 |
| 9 | Strong gale | 20.8 to 24.4 |
| 10 | Storm | 24.5 to 28.4 |
| 11 | Violent storm | 28.5 to 32.6 |
| 12 | Hurricane force | 32.7 and above |
In Beaufort mode the first class runs from your calm limit up to 1.6 m/s, so with the default calm limit of 0.5 m/s it holds the upper part of force 1. The calm limit then has to stay below 1.6 m/s.
Seasonal and night wind roses
A wind rose for the whole year can hide the wind you actually design for. The breeze that cools a building in summer often comes from a different direction from the cold wind of winter, and an annual rose averages them into something that matches neither. Use the Months menu to draw December to February, March to May, June to August or September to November, or pick any set of months yourself, and compare the roses side by side.
The hour filter does the same for the time of day. From 20:00 to 06:00 shows the night winds that matter for night ventilation and thermal mass; the filter wraps past midnight. The middle of the day shows the wind that people on a terrace will feel. NASA POWER hours are in local solar time, without daylight saving, so they can differ from clock time by an hour or more depending on where the site sits in its time zone.
Filters need dates. NASA POWER and EPW data always have them; a CSV file needs a date column for the month and hour filters to work, and without one the chart says it has no time filter.
Where the wind data comes from
NASA POWER, from the NASA Langley Research Center, publishes hourly wind at 10 m above ground from the MERRA-2 reanalysis, for any point on earth, from 2001 onwards. It is free and public. The values are averages over a grid cell of about 0.5° by 0.625°, not measurements from a station, so the wind they describe is the wind over open terrain at that scale. An airport station a few kilometres away can show a different pattern, especially on coasts, in valleys and between hills.
When a better local source exists, use it.
- EPW file: the weather files used for energy simulation contain an hourly wind direction and speed for one typical year. Free collections such as climate.onebuilding.org cover stations around the world. The site’s coordinates are taken from the file.
- CSV file: one row per record with the direction in degrees, where the wind comes from with 0 as north, and the speed. Choose the speed unit used in the file. An optional first column with dates enables the month and hour filters; the tool reads YYYY-MM-DD HH, YYYYMMDDHH, DD/MM/YYYY HH and MM/DD/YYYY HH, detects the day and month order where it can, and lets you set it under Dates in the file. Commas, semicolons and tabs all work as separators.
As a cross check, the 2025 NASA POWER wind for Istanbul and the Istanbul Atatürk typical year EPW file give the same pattern: a dominant north northeast to northeast wind and a secondary southwest wind.
Putting the wind rose on a site analysis sheet
On a site analysis board the wind rose usually sits next to the sun path, because the two together decide most of the orientation questions. Draw the sun path for the same site with the sun path diagram generator, and the monthly temperature and rainfall with the climate graph generator.
On the site plan itself, a wind rose works best as arrows: a bold arrow for the prevailing wind in summer, another for the winter wind, both drawn from the direction the wind comes from. Keep the legend with the speed classes and the source line that the tool prints on the image, “Data: NASA POWER (NASA Langley Research Center)”, with the year. For the other layers of the study, our roundup of site analysis tools for architects covers what else to bring in.
What this wind rose does not tell you
Reanalysis wind is smoothed. It describes the regional wind at 10 m over open ground, and the buildings, trees and landform around your site change it: streets channel it, tall blocks pull it down to the ground, and a hill can shelter one side of the site and expose the other. For wind comfort around tall buildings you need a wind study on the actual massing.
Nor is a wind rose a basis for structural wind loads. Those come from the design wind speed in the building code that applies to the project, such as ASCE 7 in the United States or EN 1991-1-4 in Europe. Use this tool for early design: orientation, openings, outdoor space and shelter.
Frequently asked questions
What is a wind rose?
A circular chart that shows how often the wind blows from each direction and at what speed, over a chosen period. The longest spoke is the prevailing wind.
Is the wind direction where the wind comes from or where it goes?
Where it comes from. A north wind blows from the north, and the north spoke counts the hours when the wind came from that direction.
Where does the wind data come from?
From NASA POWER, the hourly MERRA-2 reanalysis published by NASA Langley Research Center, which is free and public. You can also use your own EPW or CSV file.
What does calm mean?
Hours with wind below the calm limit, 0.5 m/s by default in every speed unit. You can change the limit. Calm hours have no direction and are shown in the centre. Changing the speed unit does not change the calm share or the speed classes, only their labels.
Can I use it for any city?
Yes. Any coordinates on land or sea work, and the city list is only a shortcut. NASA POWER data starts in 2001.
Can I use the image in my portfolio or thesis?
Yes. NASA POWER data is public. Keep the source line “Data: NASA POWER (NASA Langley Research Center)” on the image or in your caption.
