A Simm is a six-hundred metre summit in Britain with a drop of 30 metres all round. The name was changed from Sim to Simm in December 2015. At the end of 2016 there were 2531 Simms, including 767 Marilyns and a further 349 Humps.
Simms were introduced as a hill category in 2010, to incorporate and rationalise an unwieldy assortment of several categories, including Murdos, Corbett Tops (CTs), Graham Tops (GTs), SubGTs, Welsh Hewitts, English Hewitts and Subhewitts. These hill listings were published in a series of five TACit Tables published by TACit Press from 1995 to 2004. This update summarises the changes to these TACit Tables since publication:
| TACit Table | Year | Total then | Total at end 2016 |
| The Murdos | 1995 | 444 | 443 |
| Corbetts Tops and Corbetteers | 1999 | 668 | 676 |
| Graham Tops and Grahamists | 2004 | 999 | 997 |
| 600-609.6m in Scotland | 2004 | 74 | 74 |
| The Hewitts and Marilyns of Wales | 1997 | 137 | 137 |
| 600-609.6m in Wales | 1997 | 15 | 14 |
| The Hewitts and Marilyns of England | 1997 | 178 | 179 |
| 600-609.6m in England | 1997 | 14 | 13 |
| Total Simms | 2527 | 2531 |
Windy Gyle and The Schil are on the Scotland / England border and are counted only once in the overall total.
The following Simms have been discovered since 2004. Height and drop are given to the nearest 0.1m if they are derived from accurate hill surveys.
| Section | Height | Number | Name | Map | Grid Ref | Drop |
| 01A | 648.3 | 5645 | Sron Mhor | 51 | NN642272 | 32.4 |
| 01C | 710.5 | 5729 | Stob Glas | 50,56 | NN365200 | 30.9 |
| 01C | 661.7 | 5738 | Meall an Lochain | 51 | NN511237 | 30.3 |
| 01C | 619.2 | 5745 | Creag na h-Iolaire | 51 | NN561257 | 31.7 |
| 02B | 951.4 | 155 | Beinn nan Eachan East Top | 51 | NN574383 | 30.1 |
| 02B | 892.5 | 5843 | Cam-Chreag | 51 | NN524398 | 31.3 |
| 03A | 906.2 | 3664 | Aonach Eagach East Top | 41 | NN155582 | 33.1 |
| 03B | 734.2 | 5874 | Sgorr Dhonuill Far West Top | 41 | NN024565 | 30.9 |
| 06A | 756.5 | 5985 | An Sgarsoch Far East Top | 43 | NN961851 | 36.0 |
| 06A | 792.1 | 5982 | Carn Dearg | 35,43 | NN812904 | 33.1 |
| 06B | 817.6 | 6006 | Carn Bhac South Top | 43 | NO042809 | 30.5 |
| 07A | 864.6 | 6054 | Carn Ait | 43 | NO142734 | 32.0 |
| 08A | 783.0 | 6154 | Carn Ban Mor West Top | 36 | NN875979 | 30.8 |
| 08B | 721.4 | 6169 | Little Garvoun | 36 | NJ132090 | 31.4 |
| 09A | 602.6 | 6203 | Cnapan a'Choire Odhair Mhoir | 36 | NH904299 | 36 |
| 09B | 879 | 4382 | Carn Leac East Top | 34 | NN412978 | 33 |
| 09B | 875.8 | 6233 | Carn na Criche | 35 | NH576008 | 33.1 |
| 10A | 633.4 | 4267 | Beinn Aoidhdailean | 33 | NG886140 | 33.3 |
| 10A | 614.1 | 4270 | Sgurr Mor Near West Top | 33 | NG875079 | 31.4 |
| 10B | 877 | 6375 | Sgurr a'Choire-bheithe East Top | 33 | NG900012 | 31 |
| 12A | 1005.2 | 891 | Creag Toll a'Choin | 25 | NH130453 | 402 |
| 14A | 960.4 | 1016 | Glas Mheall Liath | 19 | NH077841 | 32.4 |
| 17B | 829.7 | 6855 | Caisteal a'Garbh-choire | 32 | NG454202 | 31.7 |
| 19C | 645.4 | 6962 | Cruach Fhiarach | 56 | NN256029 | 31.4 |
| 20C | 653.2 | 6999 | Meall Donn | 69 | NR906450 | 30.4 |
Sgurr Mor Far West Top (10A) was added in 2012 but removed after a survey in 2015.
The following hills listed in TACit Tables have less than 30m drop or are under 600m high and are not Simms.
| Section | Height | Num | Name | Map | Grid Ref | Drop |
| 01A | 598.2 | 5655 | Creag Liath | 52 | NN913334 | 29.5 |
| 01B | 753.6 | 3930 | Leacann Amarach | 57 | NN615164 | 29.2 |
| 01C | 707.0 | 3961 | Meall Sgallachd | 51 | NN553259 | 28.8 |
| 02B | 808.4 | 2984 | Meall Eoghainn | 51 | NN468323 | 29.8 |
| 03A | 866.3 | 2989 | Stob Dubh | 41 | NN151588 | 28.2 |
| 03B | 1106.9 | 193 | Stob Coire nam Beith | 41 | NN138546 | 28.1 |
| 03C | 995.5 | 246 | Stob a'Ghlais Choire | 41 | NN239516 | 25.8 |
| 03C | 746.8 | 4029 | Creag Dhubh | 41 | NN258520 | 28.8 |
| 06A | 753.5 | 4060 | An Sgarsoch East Top (superseded) | 43 | NN953847 | 27.9 |
| 06B | 706.7 | 4090 | Meall na h-Eilrig | 43 | NN975716 | 28.9 |
| 07A | 871.9 | 3090 | Crow Craigies South Top | 44 | NO229790 | 28.6 |
| 09B | 909.9 | 630 | Meall a'Bhothain | 35 | NH663056 | 29.6 |
| 12A | 1004.9 | 890 | Maoile Lunndaidh (superseded) | 25 | NH135458 | 10.5 |
| 12B | 713 | 4366 | Sgorr na Diollaid Far West Top (point 713m) | 25 | NH264359 | 28 |
| 12B | 598.7 | 947 | Meallan Odhar Doire nan Gillean | 25 | NH156377 | 177 |
| 15A | 884 | 3267 | Beinn Dearg North Top | 20 | NH265819 | 27 |
| 15B | 688.8 | 3660 | Sidhean a'Choin Bhain | 21 | NH600803 | 29.7 |
| 16B | 715.1 | 4466 | Carn an Tionail | 10 | NC575476 | 29.6 |
| 16B | 599.7 | 1136 | Meallan Liath | 9 | NC514503 | 147.3 |
| 18A | 677.4 | 4508 | Sgurr Dhomhuill Beag | 40 | NM743756 | 29.3 |
| 19C | 643.4 | 4535 | Beinn Lochain East Top | 56 | NN164003 | 26.2 |
| 30F | 683.7 | 2143 | Gau Graig | 124 | SH743141 | 25.4 |
Suie Dhu (11A) was demoted in 2013 but reinstated after a survey in 2014. Carn Chomh-Stri (7A) and Bera Mawr (30B) have both had surveys indicating that they have less than 30m drop, but remain Simms pending resurveys to confirm the results.
There have been several summit relocations where the highest point has been changed to a nearby grid reference on the same hill. Selected new heights and grid references are shown below.
| Section | Height | Name | Map | Grid Ref | Drop | |
| 01A | 620.3 | 3924 | Meall nam Fiadh (was Creag Odhar) | 51 | NN691272 | 67.7 |
| 01A | 618.6 | 3925 | Meall nam Fiadh Far East Top | 51,52 | NN707272 | 46.1 |
| 01B | 617.9 | 3949 | Sron na Maoile | 57 | NN690177 | 36.5 |
| 01D | 629.9 | 3983 | Beinn Bhreac | 50,56 | NN202216 | 92.8 |
| 02A | 736.5 | 3994 | Creag an Loch | 52 | NN823544 | 95.7 |
| 06A | 887.0 | 3041 | Elrig 'ic an Toisich | 43 | NN865788 | 34.2 |
| 09B | 633.2 | 4249 | Carn Glac an Eich | 26,35 | NH694267 | 81.8 |
| 10B | 898 | 744 | Sgurr nan Eugallt | 33 | NG927048 | 612 |
| 10B | 740 | 4276 | Meall a'Choire Dhuibh | 33,40 | NM917979 | 101 |
| 13B | 627 | 996 | Beinn na Feusaige | 25 | NH090542 | 226 |
| 21A | 718.4 | 4550 | The Socach | 37 | NJ279145 | 87 |
| 27C | 664 | 1754 | Scaw'd Law | 78 | NS922038 | 58 |
| 28B | 800.8 | 1836 | Lochcraig Head | 79 | NT166177 | 108 |
| 28B | 729.9 | 1852 | Swatte Fell | 78 | NT118113 | 36.3 |
| 30F | 678.5 | 2145 | Maesglase | 124,125 | SH817150 | 318 |
| 32A | 802.6 | 5603 | Fan Brycheiniog | 160 | SN824220 | 424 |
| 35B | 628.0 | 2793 | Gragareth | 98 | SD687793 | 32.8 |
The summit of The Saddle was moved to the rock next to the trig pillar in 2013 but moved back to its original correct location following a survey in 2014. The summit of An Dun was moved back to its original location (the south summit) following a GNSS survey in 2016 that supported the result of a 2009 survey, although the difference was only 1-3cm.
Numerous Simms have been renamed since the publication of TACit Tables. Selected changes are shown below.
| Section | Height | Name | Map | Grid Ref | Drop | |
| 01B | 708.3 | 3937 | Creag na h-Eararuidh (was Stuc na Cabaig) | 57 | NN685190 | 353 |
| 01C | 941.4 | 2925 | Beinn a'Chroin (was Beinn a'Chroin West Top) | 50,56 | NN387185 | 137.1 |
| 01C | 940.1 | 36 | Beinn a'Chroin East Top (was Beinn a'Chroin) | 50,56 | NN393185 | 63.1 |
| 02A | 796.5 | 2973 | Creag a'Chaorainn (was Meall Phubuill) | 51 | NN442438 | 90.4 |
| 07A | 845.5 | 3096 | Craig Damff (was Cairn Damff) | 44 | NO247777 | 33.6 |
| 15A | 667 | 1077 | Beinn Bhreac (was Meall Dubh) | 20 | NH225886 | 158 |
| 15A | 646 | 4428 | Meall Dubh (was Meall Dubh North Top) | 20 | NH214900 | 54 |
| 17D | 702 | 1294 | Trollabhal (Rum) (was Trallval) | 39 | NM377952 | 190 |
| 30E | 607.8 | 2126 | Y Garn (was Glan-hafon) | 125 | SJ080272 | 84 |
| 30E | 600.8 | 2128 | Cefn Perfedd (was Moel yr Henfaes East Top) | 125 | SJ099373 | 32.3 |
| 30F | 661 | 2149 | Craig-las (was Tyrrau Mawr) | 124 | SH677135 | 103 |
| 31A | 684 | 2164 | Drum Peithnant (was Y Garn) | 135 | SN775851 | 56 |
| 35A | 609.6 | 2770 | Thack Moor (was Renwick Fell) | 86 | NY611462 | 58 |
There have been changes to the height of numerous Simms since the TACit Tables were published. Current details are available in the Database of British and Irish Hills and via the hill-bagging.co.uk website. Some notable height or drop changes are shown below.
| Section | Old | New | Name | Map | Grid Ref | Drop |
| 1B | 705 | 708.3 | Creag na h-Eararuidh | 57 | NN685190 | 353 |
| 1B | 706 | 706.6 | Beinn Dearg | 57 | NN696197 | 73.4 |
| 1D | 870 | 852.4 | Stac a'Chuirn | 50,56 | NN190180 | 34.9 |
| 2B | 1118 | 1123.11 | Meall Garbh | 51 | NN644437 | 198 |
| 2B | 1118 | 1117.11 | An Stuc | 51 | NN638431 | 126 |
| 2B | 916 | 914.3 | Creag na Caillich | 51 | NN562377 | 69.3 |
| 3C | 1009 | 1024.3 | Drochaid Ghlas | 50 | NN083307 | 90.5 |
| 5B | 914 | 914.6 | Carn na Caim South Top | 42 | NN663806 | 30.4 |
| 7A | 611 | 609.1 | Corwharn | 44 | NO288651 | 152 |
| 8B | 862 | 863.0 | Creag an Dail Bheag | 36,43 | NO157981 | 211 |
| 8B | 862 | 861.5 | Carn Liath | 36,43 | NO164976 | 33.2 |
| 10A | 885 | 885.5 | Buidhe Bheinn | 33 | NG963090 | 160 |
| 10A | 885 | 885.2 | Sgurr a'Bhac Chaolais | 33 | NG958110 | 121 |
| 12A | 915 | 913.4 | Sgurr nan Ceannaichean | 25 | NH087480 | 185 |
| 13B | 762 | 761 | A'Chioch | 24 | NG810446 | 38 |
| 14A | 916 | 914.1 | Beinn a'Chlaidheimh | 19 | NH061775 | 268 |
| 17B | 912 | 914.2 | Knight's Peak | 32 | NG471254 | 44 |
| 17B | 898 | 900.1 | Sgurr a'Bhasteir | 32 | NG464257 | 30.1 |
| 17C | 610 | 609.0 | Ben Aslak | 33 | NG750191 | 329 |
| 19C | 761 | 763.5 | Cnoc Coinnich | 56 | NN233007 | 273.5 |
| 19C | 658 | 658.3 | Stob na Boine Druim-fhinn | 56 | NN168025 | 149.4 |
| 21A | 610 | 609.1 | Ladylea Hill | 37 | NJ343168 | 200.9 |
| 27B | 786 | 786.8 | Kirriereoch Hill | 77 | NX420869 | 150.2 |
| 30B | 999 | 1000.8 | Glyder Fawr | 115 | SH642579 | 642 |
| 30B | 609 | 609.8 | Mynydd Graig Goch | 115,123 | SH497485 | 71 |
| 30E | 620 | 630.1 | Pen yr Allt Uchaf | 124,125 | SH871196 | 70 |
| 35A | 609 | 609.6 | Thack Moor | 86 | NY611462 | 58 |
| 35B | 609 | 610.4 | Birks Fell | 98 | SD918763 | 158 |
These are the Simms with the greatest relative height.
| Section | Height | Name | Map | Grid Ref | Drop |
| 4A | 1344.5 | Ben Nevis | 41 | NN166712 | 1344.5 |
| 11A | 1182.8 | Carn Eige | 25 | NH123261 | 1146 |
| 30B | 1084.7 | Snowdon | 115 | SH609543 | 1039 |
| 17B | 992.0 | Sgurr Alasdair | 32 | NG450207 | 992.0 |
| 1C | 1174 | Ben More | 51 | NN432244 | 985 |
| 17E | 966.9 | Ben More (Mull) | 47,48 | NM525330 | 966.9 |
| 13A | 1055 | Spidean a'Choire Leith, Liathach | 25 | NG929579 | 957 |
| 8A | 1309 | Ben Macdui | 36,43 | NN989989 | 950 |
| 14B | 1110 | Sgurr Mor | 20 | NH203718 | 915 |
| 2B | 1214 | Ben Lawers | 51 | NN635414 | 915 |
| 34B | 978.1 | Scafell Pike | 89,90 | NY215072 | 912 |
| 3C | 1127.0 | Ben Cruachan | 50 | NN069304 | 880 |
These Simms are less than 601m high.
| Section | Height | Name | Map | Grid Ref | Drop |
| 09B | 600.4 | Beinn Bhreac | 35 | NH757276 | 33.4 |
| 17E | 600.8 | Cruachan Beag | 47,48 | NM578338 | 34.4 |
| 27C | 600.5 | Hare Hill | 71,77 | NS654097 | 74 |
| 30B | 600.2 | Foel Lwyd | 115 | SH720723 | 51 |
| 30E | 600.8 | Cefn Perfedd | 125 | SJ099373 | 32.3 |
| 30E | 600.4 | Y Gribin | 124,125 | SH843177 | 34.1 |
| 32C | 600 | Craig y Llyn | 170 | SN906031 | 392 |
| 34D | 600 | Black Combe | 96 | SD135854 | 362 |
A Subsimm is a hill at least 600m high with a drop all round of 20-29.9m. There are currently 665 Subsimms. Over 200 of these have been surveyed to show that they have less than 30m drop. There are 23 unsurveyed hills with a drop of 29m and another 23 with a drop of 30m, so there will undoubtedly be further changes to the Simms and Subsimms in future.
Membership of the Simm Hall of Fame is open to anyone who has climbed over 2000 Simms. By the end of 2016 there were nine members. A further 19 people have reported climbing over 1500 Simms and have therefore entered the Corridor that leads to the Simm Hall of Fame. Anyone eligible to join the Hall or Corridor should contact the author via email to rhb@rhb.org.uk.
Thanks are due to Myrddyn Phillips for surveys of several Simms that have confirmed their status and produced accurate height and drop data, and to GJ Surveys for their survey of Gau Graig. All other surveys leading to changes in Simm status have been carried out by Alan Dawson. Thanks also to Jim Bloomer, Chris Crocker and Mark Jackson, who have helped to discover potential new Simms or new summits for existing Simms by studying OS maps.
