Clothes Sun Dry Time

Sun drying times for clothes

How fast laundry dries outside comes down to four things: temperature, relative humidity, wind and fabric weight. Take a sunny day around 25-30°C with a bit of breeze. A cotton T-shirt is done in 2-3 h, jeans need 4-6 h, and a thick towel can run 6-8 h. The rough relationship is time ∝ mass_of_water / (vapour_pressure_deficit × air_flow). When humidity climbs past 80% the time roughly doubles, since the air is already close to saturation and has little room left for more moisture. Direct sun speeds up evaporation, but the UV also fades dark or printed fabrics, so those tend to do better in ventilated shade. For instance, a cotton T-shirt at 28°C and 60% RH dries in about 2.5 h; bump the humidity to 85% at the same temperature and it stretches to roughly 5 h.

Applications

Handy for planning the household wash, for laundromats and hotels working out how much clothesline they need, and for weighing the cost of a tumble dryer (one cycle burns 2-4 kWh, while the line costs nothing). It also helps when you are camping or planning anything outdoors.

FAQ

Why does jeans take so much longer than a T-shirt? Denim is thick and heavy, so each pair soaks up far more water than a thin shirt. And the inner layers only start drying once the outer ones have given up their moisture.

Is direct sun bad for clothes? Over time UV fades dyes and weakens elastane. If you want colours to last, turn dark items inside out or hang them in ventilated shade.

What if it is humid but windy? Wind goes a long way toward offsetting humidity. It strips away the saturated layer of air sitting right against the fabric, so a breezy 80% RH day will often dry faster than a still 60% RH one.