When Bitcoin appeared in 2009, the capacity of each block of 10 minutes was 32mb which can be conversed to be 200tps, transactions per second. However, after that, the founder of Bitcoin Satoshi Nakamoto decreases the limitation to be 1 mb in order to prevent system to be attacked. From then on, the system of Bitcoin can deal with 7tps at most. By comparison with 1000tps of Alipay and 4000tps of VISA, it is little.
It's not even near 7tps, more like
2.7tps. A couple of months ago I sampled six days worth of blocks which were >90% full.
Block_height Block_time Size_KB Num_Tx Fee_BTC
341192 31/01/2015_7:10 976.54 2518 0.3303735
341226 31/01/2015_13:01 903.09 1106 0.15922165
341305 1/02/2015_1:05 959.89 1320 0.20086461
341313 1/02/2015_2:19 912.48 693 0.2979134
341350 1/02/2015_7:49 975.67 1735 0.263689
341505 2/02/2015_5:11 976.5 735 0.16244257
341517 2/02/2015_7:02 947.72 746 0.14308729
341519 2/02/2015_7:36 957.16 482 0.13242593
341520 2/02/2015_8:02 976.45 1964 0.28018485
341525 2/02/2015_8:35 973.77 844 0.187877
341737 3/02/2015_19:00 976.49 1291 0.18828618
341765 4/02/2015_1:23 976.49 2549 0.35075577
341773 4/02/2015_2:45 941.58 1635 0.22893775
341794 4/02/2015_6:05 976.46 2380 0.31873266
341798 4/02/2015_6:50 971.04 1759 0.24739191
341810 4/02/2015_8:30 976.17 1705 0.25575189
341944 5/02/2015_4:08 976.54 2268 0.30628975
341951 5/02/2015_5:35 974.37 1635 0.23624007
341963 5/02/2015_7:53 976.46 1911 0.27444743
341965 5/02/2015_8:33 976.52 2105 0.2951799
341967 5/02/2015_9:24 973.82 2675 0.33440304
Average block size = 965KB
Average number of tx = 1622 (or approximately 2.7 tps)
Average block total fee = 0.25 BTC
The significant finding is that 20MB is a bit of a magic number for the long-term goal of getting fees towards replacing block rewards for miners.
20MB blocks would offer 54 tps and an average total fee per block of 5 BTC (based on this evidence) which means that fees would be comparable with the reward once the average block size hits 20MB and the reward is down to 6.25 BTC (within 6 years time).