Materials

Use this chart to determine the equivalent thickness of RHA steel:

material	multiplier	density
composite laminates	2	7
aluminum foam	1.33	1.25
aluminum-ceramic	0.8	1.8
HHA steel; titanium	1.5	8; 4.5
RHA steel, Krupp armor steel	1	7.86
mild steel, aka boilerplate	0.5 - 0.8	7.8
1960s aluminum armor	0.8	2.5
Harvey armor steel	0.76	~7.8
compound armor (steel over wrought iron)	0.48	~7.8
wrought iron	0.39	7.8
granite	0.2	2.7
superdense iron-aggregate concrete	~0.3	5.3
dense concrete	0.15	3.4
brick masonry with cement mortar	0.14
brick masonry with lime mortar	0.13
concrete (1:3:5 cement:sand:gravel)	0.11	2.4
broken stone or gravel, 1" across	0.066
adobe bricks (varies a lot)	~0.05	~1.52
broken hard coal between 1" boards	0.035	1.11
dry sand	0.035
wet sand	0.021
dirt, loam	0.016
oak, pine	0.012	0.8
snow, compacted	0.0017	0.2
hay	0.0015	0.17

RHA stands for "rolled homogenous armor"; HHA stands for "high hardness armor". Cadloy (used in Cadillac-Gage armored vehicles) is a high hardness armor steel, with a density of 8.1.

Example: a 6" thick wall of ordinary concrete. That's 152mm, multiplied by 0.11, gives the equivalent thickness of RHA steel as 16.8mm.

Armor Conversion

For values between two listed Armor Values, use the lower value. Don't add Armor Values together -- it's not a linear scale. Instead, determine the RHA equivalents, add those together, and use the Armor Value for the total. For layered fabric armor, it's best to use known examples.

RHA steel, mm	CoC Armor Value
0.6	5
0.75	6
1	7
1.5	8
2	9
2.5	10
4	11
4.5	12
5	13
6	14
7.5	15
10	16
11	17
12.5	18
15	19
16	20
17.5	21
20	22
25	23
30	24
35	25
40	26
45	28
50	31
75	37
100	42
125	46
150	51
175	56
200	61
225	67
250	72
275	78
300	83
325	89

Example: 16.8mm of RHA steel has an armor value of 20.

Armor Examples

Body Armor

15th Century mild steel breastplate: 7 (2mm of very mild steel)
20th Century steel military helmet: 5 (0.9 to 1.1 mm of good steel; M1 helmet weighs 1.6 kg)
M69 vest (Vietnam period): 5 flex (12 layers of ballistic nylon, 4.6 kg mass in medium size)
PASGT vest (Eighties military): 6 flex (13 layers of kevlar, weighs 4.1 kg in medium size)
PASGT "fritz" helmet (US military after 1983): 9 (kevlar fiberglas, 1.6 kg with suspension, straps, etc.)
CVC Fragmentation Protective Undergarment: 6 flex (14 layers of kevlar, weighs about 1 kg)
DH-132 CVC helmet: 5 (fiberglas shell, weighs 2 kg)
NIJ Level I body armor: 6 flex (7 to 12 layers of kevlar, vest about 1 kg)
NIJ Level IIA body armor: 7 flex (15 to 19 layers of kevlar, vest about 1.5 to 1.8 kg)
NIJ Level II body armor: 9 flex (20 to 24 layers of kevlar, vest about 1.8 kg to 2.3 kg)

NIJ Level IIIA body armor: 10 flex (28 to 38 layers of kevlar, vest about 2.8 to 3.5 kg)
chest or back plate to wear in body armor: 13 (5mm plastic-coated steel, 25 x 25 cm, weight 2.7 kg)

note the plate only covers the chest location, not the abdomen

NIJ Level III body armor: 12 flex (lots of layers of kevlar, perhaps with steel or ceramic inserts in which case NOT flex)
NIJ Level IV body armor: 14 or 15 (6mm steel or ceramic inserts, with kevlar or ballistic nylon carrier)
HAAM suit: 25 (materials undisclosed)
Morrow Project coverall: 7 flex (1 layer of resistweave cloth, weight 1.71 kg)

worn over a CVC armor vest, the chest and abdomen get a total armor value of 9 flex
two layers of resistweave is also armor value 9 flex
four layers of resistweave, armor value 10 flex

leather military boot, with steel-capped toe and armored sole: 4 (weight 1.52 kg per pair), flex on top

Body armor weights are for some Eighties examples; there's a lot of variety in coverage, tailoring, materials and of course sizing. Ballistic nylon and kevlar degrade significantly from UV exposure, not to mention normal wear and abrasion. A vest used for 5 years in the sun will have lost 1 point of armor value. By the time the vest loses any more armor value (after another 5 years outdoors) it will be falling apart at the seams anyway.

Resistweave fabric is fire resistant, and doesn't degrade from UV exposure. It's a fairly bulky fabric - a single-layer vest would weigh 0.8 kg, about eight times what one layer of kevlar would weigh.

Vehicles

Tiger I tank hull front: 42 (100mm homogenous armor plate)
M60 tank hull front: 51 (155mm homogenous armor plate)
Iowa-class battleship hull side: ~125 (307mm hard homogenous armor plate, behind 38mm steel)
Sherman M4A3: front hull 34 (64mm RHA steel), hull side 25 (38mm RHA steel), turret front 40 (92mm RHA steel), turret side 31 (50mm RHA steel)
A-10 Thunderbolt II cockpit tub: 32 (38mm titanium)
Me-108 fuselage: 4 (0.64mm aircraft aluminum)
M113 armored personnel carrier: 23 (35mm aluminum armor alloy)
MARS-ONE: 50 (25mm aluminum, air space, 75mm boron carbide/carbon fiber mesh, 25mm high hardness steel)
Commando V-150, Commando Scout, Commando Ranger: 16 (6.4mm high hardness Cadloy steel), 21 underneath (12.7mm high hardness Cadloy steel)

note that the V-150 and Scout have some nicely angled surfaces, which can increase effective hull armor to 18 or 19 against "horizontal" attacks.

Scientific-One, Overland Train: 18 (8.3mm high-hardness Cadloy steel, plus a polyethylene spall liner)
Morrow Project SK-5 hovercraft: 15 (10mm aluminum alloy armor)
USS Constitution: 14 (21" oak)
very sturdy old truck cab: 6 (1.2mm mild steel, based on 1948 Studebaker)
1980s sedan body: 5 (0.76mm mild steel)
dump-truck body: 10 (10 gauge sides, 7 gauge floors of mild steel)
railway boxcar sides: 9 (2.5mm mild steel)

Structures and Terrain

sandbag: 17 (305mm thick, filled with sand)
"American bond" brick wall: 23 (203mm thick)
cement block, as masonry: 20 (203mm thick, core filled with grout and rebar)
cement block, loose: 14 (203mm thick, but empty core takes up half the thickness)
14" thick adobe wall: 21
11' thick adobe wall: 53
1/2" mild steel plate: 16
diamond plate: 9 to 12 (3mm to 6mm mild steel)
6" thick pine or oak: 8
18 gauge mild steel (1.27mm) -- quonset hut material: 7