The weather affects how we feel, how safe it is to be outside, and how our gardens grow, and a few calculations make sense of all three. This guide explains the key weather metrics — what they mean and when they matter — and the garden maths that goes with them.
Why it feels colder than it is
On a windy day the air feels colder than the thermometer reads, because moving air strips heat away from your skin faster than still air. Wind chill captures this 'feels like' temperature from the actual air temperature and the wind speed. It is more than a comfort figure: at low temperatures, a strong wind chill sharply raises the risk of frostbite and hypothermia, which is why winter warnings quote it. The wind chill calculator works it out, so you can dress for how cold it really feels rather than the number on the thermometer.
Why it feels hotter than it is
In summer the opposite happens: high humidity makes it feel hotter, because your sweat cannot evaporate to cool you when the air is already moist. The heat index combines temperature and humidity into a feels-like figure, and it can climb to genuinely dangerous levels where heat exhaustion and heatstroke become real risks. The heat index calculator shows when to take care — to slow down, seek shade and drink more water — on a hot, humid day.
Dew point and humidity
Dew point is the temperature at which the air becomes saturated and water condenses out as dew. It is a steadier, more intuitive measure of how muggy it feels than relative humidity, because relative humidity changes through the day as the temperature does, while dew point stays put. A dew point below about 13°C feels comfortable, while above 20°C feels oppressive. The dew point calculator estimates it from temperature and humidity, and it also tells you when dew, fog or condensation are likely.
Frost, dew and your garden
These same numbers matter to gardeners. When the temperature falls to the dew point and that point is below freezing, frost forms — a serious threat to tender plants. Knowing the forecast dew point and overnight low helps you decide when to cover seedlings or hold off planting. Understanding the weather is the first half of gardening well; the second half is getting the watering and growing maths right.
Watering your garden
Plants need a surprising amount of water, and both over- and under-watering cause problems — shallow roots, disease and waste. The amount depends on the area and the depth of water you want to apply; many gardens do well with around 25 mm of water a week, delivered as a deep soak a couple of times rather than a daily sprinkle that keeps roots near the surface. The watering requirement calculator turns area and depth into litres, so you water purposefully.
Harvesting rainwater
Much of that water can come free from the sky. The rain falling on a roof is simply its area multiplied by the rainfall depth, and even modest roofs collect a surprising volume — a millimetre of rain on a 100-square-metre roof is 100 litres. Storing it in a butt or tank cuts your water bill and gives plants the soft, unchlorinated water they prefer. The rainwater harvesting calculator estimates how much your roof can collect from your local rainfall.
Frost dates and the growing season
For gardeners, the calendar matters as much as the thermometer. The length of your growing season — the stretch between the last frost of spring and the first of autumn — decides what you can grow and when to sow. Planting tender crops before the last frost risks losing them in a single cold night, while sowing too late leaves slow growers no time to mature. Watching the overnight low against the dew point warns when frost is likely, so you can cover seedlings or delay planting. Knowing your local frost dates, and counting the frost-free days between them, turns guesswork into a planting plan that works with your climate rather than against it.
Sowing and spacing
A healthy garden also starts with the right amount of seed and the right spacing between plants, so they have room to grow without competing for light, water and nutrients. The grass seed calculator works out how much seed a lawn needs, and the plant spacing calculator tells you how many plants fit a bed. Put the weather and the garden maths together — dress for the real feels-like temperature, protect plants from frost, water deeply, harvest the rain and space your planting — and both you and your garden come through the seasons in good shape.