The following table provides the weight of water per inch per square foot in pounds. One cubic inch of water weighs 0.036127 of a pound. One square foot of water one inch deep weighs 144 times this, or 5.202288 pounds. Everything else has been calculated from this.

This table should give you an idea of how much of a live load is being added to your roof by areas of ponding water or clogged drains. (Also see Roof Online’s Roof Drainage page.)

Values for areas or depths not covered in the table should be easy to arrive at simply by adding together values for areas or depths which are covered.

Weight of Water per Inch per Square Foot in Pounds
Area in Square Feet
Depth of Water in Inches 1 Square Foot 2 Square Feet 3 Square Feet 4 Square Feet 5 Square Feet 10 Square Feet 20 Square Feet 30 Square Feet 40 Square Feet 50 Square Feet 100 Square Feet 500 Square Feet 1000 Square Feet
0.25 Inch 1.30 lbs. 2.60 lbs. 3.90 lbs. 5.20 lbs. 6.50 lbs. 13.01 lbs. 26.01 lbs. 39.02 lbs. 52.02 lbs. 65.03 lbs. 130.06 lbs. 650.29 lbs 1,300.57 lbs.
0.5 Inch 2.60 5.20 7.80 10.41 13.01 26.01 52.02 78.03 104.05 130.06 260.11 1,300.57 2,601.14
1 Inch 5.20 10.41 15.61 20.81 26.01 52.02 104.05 156.07 208.09 260.11 520.23 2,601.14 5,202.29
2 Inches 10.41 20.81 31.21 41.62 52.02 104.05 208.09 312.14 416.18 520.23 1,040.46 5,202.29 10,404.58
3 Inches 15.61 31.21 46.82 62.43 78.03 156.07 312.14 468.21 624.27 780.34 1,560.69 7,803.43 15,606.86
4 Inches 20.81 41.62 62.43 83.24 104.05 208.09 416.18 624.27 832.37 1,040.46 2,080.92 10,404.58 20,809.15
5 Inches 26.01 52.02 78.03 104.05 130.06 260.11 520.23 780.34 1,040.46 1,300.57 2,601.14 13,005.72 26,011.44
6 Inches 31.21 62.43 93.64 124.86 156.07 312.14 624.28 936.41 1,248.55 1,560.69 3,121.37 15,606.86 31,213.73
7 Inches 36.42 72.83 109.25 145.66 182.08 364.16 728.32 1,092.48 1,456.64 1,820.80 3,641.60 18,208.01 36,416.02
8 Inches 41.62 83.24 124.86 166.47 208.09 416.18 832.37 1,248.55 1,664.73 2,080.92 4,161.83 20,809.15 41,618.30
9 Inches 46.82 93.64 140.46 187.28 234.10 468.21 936.41 1,404.62 1,872.82 2,341.03 4,682.06 23,410.30 46,820.59
10 Inches 52.02 104.05 156.07 208.09 260.11 520.23 1,040.46 1,560.69 2,080.92 2,601.14 5,202.29 26,011.44 52,022.88
11 Inches 57.23 114.45 171.68 228.90 286.13 572.25 1,144.50 1,716.76 2,289.01 2,861.26 5,722.52 28,612.58 57,225.17
12 Inches 62.43 124.86 187.28 249.71 312.14 624.28 1,248.55 1,873.04 2,497.10 3,121.37 6,242.75 31,213.73 62,427.46
24 Inches 124.86 249.71 374.57 499.42 624.28 1,248.55 2,497.10 3,745.65 4,994.20 6,242.75 12,485.49 62,427.46 124,854.91
36 Inches 187.28 374.57 561.85 749.13 936.41 1,872.82 3,745.65 5,618.47 7,491.29 9,364.12 18,728.24 93,641.18 187,282.37
48 Inches 249.71 499.42 749.13 998.84 1,248.55 2,497.10 4,994.20 7,491.29 9,988.39 12,485.49 24,970.98 124,854.91 249,709.82
60 Inches 312.14 624.28 936.41 1,248.55 1,560.69 3,121.37 6,242.75 9,364.12 12,485.49 15,606.86 31,213.73 156,068.64 312,137.28