Free calculator
Workable days per month
Pick a province, a weather station and a period. You see how many days per month it rained, froze or blew hard on average in 1991–2020, and use that to work out a buffer for a job of a given number of working days. You decide which days count as not workable for your kind of work.
The fields hold an example. Choose your own province, period and threshold.
That depends on your work. You pick one threshold: days of different kinds are not added together, because they overlap.
Whole days, for example 10.
Average over 1991–2020
Buffer in working days
By month
- Chosen period
- Other months
| Month | Mean temp. (°C) | Mean lowest temp. (°C) | Rain ≥ 1 mm | Rain ≥ 10 mm | Frost (min. < 0 °C) | Min. < −5 °C | Ice day (max. < 0 °C) | Wind ≥ 5 Bft | Wind ≥ 6 Bft |
|---|
All day columns are average numbers of days per month, to one decimal. The chosen period is highlighted.
Days below your lower limit
| Month | Daily mean below the limit | Lowest temperature below the limit |
|---|
Source: KNMI, climate normals 1991–2020 (CC BY 4.0), processed by Briefbee.
Dataset climate_normals_1991_2020_climate_normals_by_station, version 1, downloaded on 2026-10-13. Processed: 23 stations and 15 series selected, the averages themselves are unchanged. Where KNMI did not count an event (“.”), we read 0 days.
Average over 1991–2020. Not a weather forecast and not advice: check a current forecast (knmi.nl) and the product instructions before you plan.
Last checked: 12 October 2026.
What you enter never leaves your browser. We count anonymously how the page is used (no cookies, no IP address).
How the arithmetic works
For each weather station, KNMI counts how many days per month in 1991–2020 had 1 mm of rain or more, frost, an ice day or a given wind force, on average. Here you see those averages per month.
The buffer divides the number of days meeting your chosen threshold by the number of days in the period and multiplies by the length of your job: working days × days meeting the threshold / days in the period. February counts as 28.25 days because the period includes leap years. For several months, the days and the month lengths are added up.
The result is an average, not a prediction. One year has far more such days, another far fewer.
Frequently asked questions
Is this a weather forecast?
No. These are averages over the years 1991–2020. They say nothing about next week's weather. Check knmi.nl when you plan.
Why can I choose only one threshold at a time?
A day with rain can also be a day with strong wind. Adding the numbers would count some days twice. That is why the buffer uses the one threshold you choose.
Why do I see a lower and an upper bound for my temperature?
The normals only count days below fixed thresholds: daily mean below 0, 5, 10, 15 and 20 °C and lowest temperature below −10, −5 and 0 °C. For a value in between, we show the two nearest counts instead of estimating.
Which weather station do I choose?
Choose the station that best fits your work location. A province usually has several stations. Coast, inland and elevation can differ.
Is my input stored?
No. The calculation runs in your browser. All KNMI figures are already in the page, nothing is fetched while you use it. We only count anonymously how the page is used (no cookies, no IP address).
Where do the figures come from?
From KNMI, the climate normals 1991–2020 by station. The source and the licence are shown next to the result.
Making quotes with your own prices?
Describe the job. Briefbee writes the quote in your words and at your prices; you check it and send it.