Clothesline Length Calculator

Clothesline length and capacity depend on the number of items you want to hang, the space each item requires, and the sag factor when a load is applied to the line.

Total line length formula: Line Length = Items × (Width per Item + Spacing) + Tie-off Allowance

The calculator fixes the spacing at 3 inches and the tie-off at 24 inches (12 per end), and it gives every item its own gap rather than only the gaps between them. That one extra gap is deliberate slack, and on a full line it is the difference between pegging the last shirt comfortably and fighting the post.

Sag compensation. The textbook answer is the catenary approximation, Sag = (Load Weight × Span²) ÷ (8 × Line Tension), but line tension is not something anyone measures in a back garden. This calculator uses the practical version instead and adds a flat 12% to the length, which sits in the middle of the 10–15% range most installation guides suggest.

Variable definitions:

• Items: total number of clothing pieces to hang simultaneously
• Width per Item: average hanging width in inches: shirts ~12″, pants/jeans ~14″, sheets ~24″, socks ~4″ per pair, towels ~18″
• Spacing: minimum gap between items, for airflow and to stop them touching. 2–4 inches is the usual advice
• Tie-off Allowance: extra line at each anchor point for knots, 6–12 inches per end
• Load Weight: total weight of wet laundry (wet clothing is 60–80% heavier than dry)

Drying time estimates by fabric type (moderate sun, light breeze):

• Cotton shirts: 1.5–3 hours
• Jeans/denim: 3–5 hours
• Towels: 2–4 hours
• Bed sheets: 2–3 hours
• Synthetic fabrics (polyester, nylon): 1–2 hours
• Wool (lay flat: do NOT hang): 4–8 hours flat-drying

Environmental drying factors:

• Temperature: higher = faster (doubles roughly every 10°C increase)
• Humidity: lower RH = significantly faster; above 85% RH drying nearly stops
• Wind: even light breeze (3–5 mph) cuts drying time by 30–50%
• Direct sunlight: UV kills bacteria but can fade colors: use shade for delicate items

Worked example: One load of laundry: 5 shirts (12″ each), 2 pairs of jeans (14″), 4 pairs of socks (4″), 2 towels (18″). Thirteen items in total, averaging 13″ wide.

• Per item with its gap: 13″ + 3″ = 16 inches
• Thirteen items: 13 × 16 = 208 inches
• Tie-off allowance: 24 inches
• Raw total: 208 + 24 = 232 inches = 19.3 feet
• Plus the 12% sag allowance: 232 × 1.12 = 260 inches ≈ 21.7 feet

Round up to the nearest stocked reel and you are buying a 25-foot clothesline. Enter 13 items at 13 inches and the calculator returns exactly this. It rounds the feet up rather than down, so it reports 20 ft raw and 22 ft with sag, because nobody has ever been annoyed by four inches of spare line.

Averaging the widths is what makes the example reproducible, and it is also close enough in practice. Mixing wide and narrow items on one line changes the total by an inch or two, not by feet, because the gaps dominate more than people expect.