Here is a basic table of dimensions that will work for Half-Life tags (sprays).

Green is the acceptable values example 144x80=11520 is less then 12288.
Red is the unacceptable values example 144x144=20736 IS NOT less then 12288.
Gray is the dimensions, height width. (NOTE: the width and Height can be interchangeable)

pixels

16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256
16 256 512 768 1024 1280 1536 1792 2048 2304 2560 2816 3072 3328 3584 3840 4096*
32 512 1024 1536 2048 2560 3072 3584 4096 4608 5120 5632 6144 6656 7168 7680 8192*
48 768 1536 2304 3072 3840 4608 5376 6144 6912 7680 8448 9216 9984 10752 11520 12288
64 1024 2048 3072 4096 5120 6144 7168 8192 9216 10240 11264 12288 13312 14336 15360 16384
80 1280 2560 3840 5120 6400 7680 8960 10240 11520 12800 14080 15360 16640 17920 19200 20480
96 1536 3072 4608 6144 7680 9216 10752 12288 13824 15360 16896 18432 19968 21504 23040 24576
112 1792 3584 5376 7168 8960 10752 12544 14336 16128 17920 19712 21504 23296 25088 26880 28672
128 2048 4096 6144 8192 10240 12288 14336 16384 18432 20480 22528 24576 26624 28672 30720 32768
144 2304 4608 6912 9216 11520 13824 16128 18432 20736 23040 25344 27648 29952 32256 34560 36864
160 2560 5120 7680 10240 12800 15360 17920 20480 23040 25600 28160 30720 33280 35840 38400 40960
176 2816 5632 8448 11264 14080 16896 19712 22528 25344 28160 30976 33792 36608 39424 42240 45056
192 3072 6144 9216 12288 15360 18432 21504 24576 27648 30720 33792 36864 39936 43008 46080 49152
208 3328 6656 9984 13312 16640 19968 23296 26624 29952 33280 36608 39936 43264 46592 49920 53248
224 3584 7168 10752 14336 17920 21504 25088 28672 32256 35840 39424 43008 46592 50176 53760 57344
240 3840 7680 11520 15360 19200 23040 26880 30720 34560 38400 42240 46080 49920 53760 57600 61440
256 4096* 8192* 12288 16384 20480 24576 28672 32768 36864 40960 45056 49152 53248 57344 61440 65536