能量密度（Energy density）是指在一定的空间或质量物质中储存能量的大小。
完全能量密度
此表给出了完整系统的能量密度, 包含了一切必要的外部条件,如氧化剂和热源。
能量密度表：
存储形式
质量能量密度 (MJ/kg)
容积能量密度 (MJ/L)
Peak recovery efficiency %
Practical recovery efficiency %
质能等价
89,876,000,000
氢核聚变（太阳的能量来源)
645,000,000
Deuterium-Tritium fusion
337,000,000
核裂变(100% 铀-235) (用于核武器)
88,250,000
1,500,000,000
天然铀 (99.3% U-238, 0.7% U-235)用于快滋生反应器[2]
24,000,000
50%
浓缩铀(3.5% U235) 用于轻水反应堆
3,456,000
30%
Hf-178m2 isomer
1,326,000
17,649,060
Pu-238 a-decay
15,500,000
天然铀 (0.7% U235) 用于 轻水反应堆
443,000
30%
Ta-180m isomer
41,340
689,964
Specific orbital energy of Low Earth orbit (approximate)
33
Cl2O7 +CH4- 计算值
17.4
Cl2O7分解---计算值
12.2
硝基甲烷
11.3
12.9
八硝基立方烷炸药--计算值
8.5
17
Tetranitrotetrahedrane explosive - computed
8.3
Heptanitrocubane explosive - computed
8.2
Dinitroacetylene explosive - computed
7.9
钠(和氯反应)
7.0349
Tetranitrocubane explosive - computed
6.95
Ammonal (Al+NH4NO3oxidizer)
6.9
12.7
Tetranitromethane + hydrazine bipropellant - computed
6.6
Hexanitrobenzene explosive - computed
6.5
奥克托今炸药 - 计算值
6.3
ANFO-ANNM
6.26
三硝基甲苯[Kinney, G.F.，K.J. Graham（1985）．Explosive shocks in air．Springer-Verlag．ISBN 3-540-15147-8． ]
4.610
6.92
Copper Thermite (Al +CuOas oxidizer)
4.13
20.9
Thermite (powder Al +Fe2O3as oxidizer)
4.00
18.4
过氧化氢分解 (as monopropellant)
2.7
3.8
纳米线电池
2.54
29
95%Template:Clarify[3]
battery, Lithium Thionyl Chloride (LiSOCl2) [4]
2.5
水220.64 bar, 373.8°CTemplate:Clarify
1.968
0.708
Kinetic energy penetrator Template:Clarify
1.9
30
battery, Fluoride ion
1.7
2.8
氢闭循环燃料电池[5]sm=n
1.62
肼(有毒)分解 (as monopropellant)
1.6
1.6
硝酸铵分解 (as monopropellant)
1.4
2.5
电容EEStor生产 (宣称值) [6]
1.2
5.7
99%
99%
Thermal Energy Capacity of Molten Salt
1
98%[7]
Molecular spring approximate
1
battery, Sodium Sulfur
0
1.23
85%[8]
battery, Lithium-manganese
0.83-1.01
1.98-2.09
锂离子电池
0.46-0.72
0.83-0.9
95%
battery, Lithium Sulphur
1.26
1.26
battery(Sodium Nickel Chloride)]], High Temperature
0.56
battery, Silver-oxide
0.47
1.8
Flywheel
0.36-0.5
5.56x45 NATO子弹Template:Clarify
0.4
3.2
镍氢电池,消费产品的低功率产品
0.4
1.55
battery, Zinc-manganese (alkaline), long life design
0.4-0.59
1.15-1.43
battery, Zinc Bromine flow (ZnBr)
0.27
battery, Nickel metal hydride (NiMH), High Power design as used in cars
0.250
0.493
battery, Nickel cadmium (NiCd)
0.14
1.08
80%
battery, Zinc-Carbon
0.13
0.331
battery, Lead acid
0.14
0.36
battery, Vanadium redox
0.09
0.1188
7070-75%
battery, Vanadium Bromide redox
0.18
0.252
80%-90%[9]
Capacitor Ultracapacitor
0.0199 [10]
0.050
Capacitor Supercapacitor
0.01
80%-98.5%[11]
39%-70%[12]
Superconducting magnetic energy storage
0.008 [13]
>95%
Capacitor
0.002 [14]
Spring power (clock spring), torsion spring
0.0003 [15]
0.0006
Storage type
Energy density by mass (MJ/kg)
Energy density by volume (MJ/L)
Peak recovery efficiency %
Practical recovery efficiency %
电池的平均单位体积或质量所释放出的电能。一般在相同体积下，锂离子电池的能量密度是镍镉电池的2.5倍，是镍氢电池的1.8倍，因此在电池容量相等的情况下，锂离子电池就会比镍镉、镍氢电池的体积更小，重量更轻。
在食品营养学的角度上，能量密度是指每克食物所含的能量，这与食品的水分和脂肪含量密切有关。食品的水分含量高则能量密度低、脂肪含量高则能量密度高。