Feat[]
Quick summary of the feat; in chapter 798 Fujitora lifts rubble from across Dressrosa including debris from the destroyed houses, the remnants of the Pica statue, and the island-spanning bridge which is partially destroyed by Doflamingo's Birdcage.
So in order to figure out how much mass he moved, we need the volumes for these three things:
Pica Statue[]
Image 1 - Pica Statue[]
Dressrosa Diameter = 18.17 km = 1496 px
Pica's Waistline Height = 33 px = 412.5 m
Pica's Waistline Height = 498 px = 412.5 m
Image 2 - Pica's Proportions[]
Arm[]
Arm Length = 858 px = 710.692771084 m
Arm Width = 212 px = 175.602409639 m
Arm Volume = 17212055 m^3
Leg[]
Leg Length = 452 px = 374.397590361 m
Leg Width = 105 px = 86.9728915663 m
Leg Volume = 2224287 m^3
Head/Neck[]
Head/Neck Height = 128 px = 106.024096386 m
Head/Neck Width = 238 px = 197.138554217 m
Head/Neck Volume = 1078740 m^3
Torso[]
Height / Weight[]
Torso Width = 452 px = 374.397590361 m
Torso Height = 321 px = 265.888554217 m
Thickness[]
Arm Length = 206 px = 710.692771084 m
Torso Thickness = 104 px = 358.79635 m
Torso Volume = 35717471 m^3
Total[]
Total Dimensions = 17212055 + 17212055 + 2224287 + 2224287 + 1078740 + 35717471 = 75668895 m^3
Total Mass = 75668895 m^3 * 2700 kg/m^3 = 204,306,016,500 kg
Dressrosa Rubble[]
Assuming that the average height of Dressrosa's buildings is 20 meters since they are comprised of multiple storeys.
Height = 20 m
Using the radius of Dressrosa to roughly get the volume of buildings in Dressrosa as a cylinder.
Radius = 9085 m
Volume = 5,185,966,794 m^3
Assuming 90% hollowness here to account for both the hollowness of the buildings themselves, and all the streets, paths, courtyards and parks, etc. that aren't occupied by buildings.
10% of 5,185,966,794 m^3 = 518,596,679.4 m^3
Mass = 518,596,679.4 m^3 * 2700 kg/m^3 = 1,400,211,000,000 kg
Dressrosa Bridge[]
Image 3 - Width/Length[]
Dressrosa Width = 307 px = 18.7 km
Dressrosa Bridge Length = 88 px = 5360.26058632 m
Dressrosa Bridge Width = 7 px = 426.384364821 m
Image 4 - Height[]
Pica's Waistline Height = 33 px = 412.5 m
Dressrosa Bridge Height = 50 px = 644.53125 m
Dressrosa Bridge Volume = 1,473,096,349.17 m^3
Assuming 30% hollowness to account for the gaps in the bridge.
70% of 1,473,096,349.17 m^3 = 1,031,167,444.42 m^3
Mass = 1,031,167,444.42 m^3 * 2700 kg/m^3 = 2,784,152,099,934 kg
Method 1 - Potential Energy[]
Image 5 - Height[]
Pica Statue = 120 px = 412.5 m
Height = 508 px = 1746.25 m
Total Mass = 204,306,016,500 + 1,400,211,000,000 + 2,784,152,099,934 + 2,784,152,099,934 = 7,172,821,200,000 kg
Energy = 9.81 * 7,172,821,200,000 * 1746.25 = 122,875,540,000,000,000 joules = 29.367958891013383749 megatons
Method 2 - Kinetic Energy[]
The onlookers note that the rubble is gathering on the east side of Dressrosa. There is no telling roughly how far every piece of rubble moved or how quickly, but assuming that the mass from each quarter travelled roughly the radius of Dressrosa towards the east side, we'll use that to get the speed for the kinetic energy for now.
Distance = 9350 m
Timeframe = 10 seconds
Velocity = 935 m/s
North Side[]
From the north side will be one quarter of the mass of rubble.
Mass = 35,0052,750,000 kg
Kinetic Energy = 0.5 * 935 * 935 * 350052750000 = 153,012,430,000,000,000 joules
South Side[]
From the south side will be the top half of the Pica statue and one quarter of the mass of rubble.
Mass = 542347616700 kg
Kinetc Energy = 0.5 * 935 * 935 * 542347616700 = 237,066,920,000,000,000 joules
West Side[]
From the west side will be one quarter of the rubble, and one of the bridges.
Mass = 3,134,204,800,000 kg
Kinetc Energy = 0.5 * 935 * 935 * 3134204800000 = 1,370,000,100,000,000,000 joules
Total Energy[]
Total Kinetic Energy = 1,760,079,500,000,000,000 joules = 420.669 Megatons
Final Results[]
Potential Energy = 29.37 Megatons [City level]
Kinetc Energy = 420.669 Megatons [Mountain level]