SRD:Table of Creature Size and Scale

Warning! The following is homebrew, and as such might not be balanced.

Table: Creature Size and Scale

This modifier applies to the bull rush, grapple, overrun, and trip special attacks. Biped's height, quadruped's body length (nose to base of tail) Assumes that the creature is roughly as dense as a regular animal. A creature made of stone will weigh considerably more. A gaseous creature will weigh much less. These values are typical for creatures of the indicated size. Most player characters are medium (indicated in green), followed by small and large (indicated in yellow). Some exceptions exist.
Size Category	AC Modifier	Special Attacks Modifier1	Hide Modifier	Height or Length2	Weight3	Space4	Natural Reach4		Carrying Capacity Multiplier
							Tall	Long	Biped	Quadruped
Fine	+8	–16	+16	6 in. or less	⅛lb. or less	½ ft.	0 ft.	0 ft.	×⅛	×¼
Diminutive	+4	–12	+12	6 in.–1 ft.	⅛lb.–1lb.	1 ft.	0 ft.	0 ft.	×¼	×½
Tiny	+2	–8	+8	1 ft.–2 ft.	1 lb.–8 lb.	2½ ft.	0 ft.	0 ft.	×½	×¾
Small	+1	–4	+4	2 ft.–4 ft.	8 lb.–64 lb.	5 ft.	5 ft.	5 ft.	×¾	×1
Medium	+0	+0	+0	4 ft.–8 ft.	64 lb.–512 lb.	5 ft.	5 ft.	5 ft.	×1	×1½
Large	–1	+4	–4	8 ft.–16 ft.	512 lb.–2 tons	10 ft.	10 ft.	5 ft.	×2	×3
Huge	–2	+8	–8	16 ft.–32 ft.	2 tons–16 tons	15 ft.	15 ft.	10 ft.	×4	×6
Gargantuan	–4	+12	–12	32 ft.–64 ft.	16 tons–128 tons	20 ft.	20 ft.	15 ft.	×8	×12
Colossal	–8	+16	–16	64 ft.–128 ft.	128 tons–1,024 tons	30 ft.	30 ft.	20 ft.	×16	×24
In official capacities, a creature's size generally does not exceed that of a colossal size. The Size categories below are for those who need to explore mathmatical hypothetical situations where a creature exceeds the standard criteria.
Colossal+1	–16	+20	–20	128 ft.–256 ft.	1,024 tons–8,192 tons	40 ft.	40 ft.	30 ft.	×32	×48
Colossal+2	–32	+24	–24	256 ft.–512 ft.	8,192 tons–65,536 tons	50 ft.	50 ft.	40 ft.	×64	×96
Colossal+3	–64	+28	–28	512 ft.–1,024 ft.	65,536 tons–524,288 tons	70 ft.	70 ft.	50 ft.	×128	×192
Colossal+4	–128	+32	–32	1,024 ft.–2,048 ft.	524,288 tons–4,194,304 tons	90 ft.	90 ft.	70 ft.	×256	×384
Colossal+5	–256	+36	–36	2,048 ft.–4,096 ft.	4,194,304 tons–33,554,432 tons	110 ft.	110 ft.	90 ft.	×512	×768
Colossal+6	–512	+40	–40	4,096 ft.–8,192 ft.	33,554,432 tons–268,435,456 tons	150 ft.	150 ft.	110 ft.	×1,024	×1,536
Colossal+7	–1,024	+44	–44	8,192 ft.–3 miles	268,435,456 tons–2,147,483,648 tons	190 ft.	190 ft.	150 ft.	×2,048	×3,072
Colossal+8	–2,048	+48	–48	3 miles–6 miles	2,147,483,648 tons–17,179,869,184 tons	230 ft.	230 ft.	190 ft.	×4,096	×6,144
Colossal+9	–4,096	+52	–52	6 miles–12 miles	17,179,869,184 tons–137,438,953,472 tons	310 ft.	310 ft.	230 ft.	×8,192	×12,288
Colossal+10	–8,192	+56	–56	12 miles–24 miles	137,438,953,472 tons–1,099,511,627,776 tons	390 ft.	390 ft.	310 ft.	×16,384	×24,576
Colossal+11	–16,384	+60	–60	24 miles–48 miles	1,099,511,627,776 tons–8,796,093,022,208 tons	470 ft.	470 ft.	390 ft.	×32,768	×49,152
Colossal+12	–32,768	+64	–64	48 miles–96 miles	8,796,093,022,208 tons–70,368,744,177,664 tons	630 ft.	630 ft.	470 ft.	×65,536	×98,304
Colossal+13	–65,536	+68	–68	96 miles–192 miles	70,368,744,177,664 tons–562,949,953,421,312 tons	790 ft.	790 ft.	630 ft.	×131,072	×196,608
Colossal+14	–131,072	+72	–72	192 miles–384 miles	562,949,953,421,312 tons–4,503,599,627,370,500 tons	950 ft.	950 ft.	790 ft.	×262,144	×393,216
Colossal+15	–262,144	+76	–76	384 miles–768 miles	4,503,599,627,370,500 tons–36,028,797,018,964,000 tons	1,270 ft.	1,270 ft.	950 ft.	×524,288	×786,432
Colossal+16	–524,288	+80	–80	768 miles and above	36,028,797,018,964,000 tons and above	1,590 ft.	1,590 ft.	1,270 ft.	×1,048,576	×1,572,864

Source: https://d20.pub/resources/table-of-creature-size-and-scale/